add textcat architectures documentation

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@ -148,11 +148,113 @@ architectures into your training config.
## Text classification architectures {#textcat source="spacy/ml/models/textcat.py"}
A text classification architecture needs to take a `Doc` as input, and produce a
score for each potential label class. Textcat challenges can be binary (e.g.
sentiment analysis) or involve multiple possible labels. Multi-label challenges
can either have mutually exclusive labels (each example has exactly one label),
or multiple labels may be applicable at the same time.
As the properties of text classification problems can vary widely, we provide
several different built-in architectures. It is recommended to experiment with
different architectures and settings to determine what works best on your
specific data and challenge.
### spacy.TextCatEnsemble.v1 {#TextCatEnsemble}
Stacked ensemble of a bag-of-words model and a neural network model. The neural
network has an internal CNN Tok2Vec layer and uses attention.
> #### Example Config
>
> ```ini
> [model]
> @architectures = "spacy.TextCatEnsemble.v1"
> exclusive_classes = false
> pretrained_vectors = null
> width = 64
> embed_size = 2000
> conv_depth = 2
> window_size = 1
> ngram_size = 1
> dropout = null
> nO = null
> ```
| Name | Type | Description |
| -------------------- | ----- | ------------------------------------------------------------------------------------------------------------------------------------------- |
| `exclusive_classes` | bool | Whether or not categories are mutually exclusive. |
| `pretrained_vectors` | bool | Whether or not pretrained vectors will be used in addition to the feature vectors. |
| `width` | int | Output dimension of the feature encoding step. |
| `embed_size` | int | Input dimension of the feature encoding step. |
| `conv_depth` | int | Depth of the Tok2Vec layer. |
| `window_size` | int | The number of contextual vectors to [concatenate](https://thinc.ai/docs/api-layers#expand_window) from the left and from the right. |
| `ngram_size` | int | Determines the maximum length of the n-grams in the BOW model. For instance, `ngram_size=3`would give unigram, trigram and bigram features. |
| `dropout` | float | The dropout rate. |
| `nO` | int | Output dimension, determined by the number of different labels. |
If the `nO` dimension is not set, the TextCategorizer component will set it when
`begin_training` is called.
### spacy.TextCatCNN.v1 {#TextCatCNN}
> #### Example Config
>
> ```ini
> [model]
> @architectures = "spacy.TextCatCNN.v1"
> exclusive_classes = false
> nO = null
>
> [model.tok2vec]
> @architectures = "spacy.HashEmbedCNN.v1"
> pretrained_vectors = null
> width = 96
> depth = 4
> embed_size = 2000
> window_size = 1
> maxout_pieces = 3
> subword_features = true
> dropout = null
> ```
A neural network model where token vectors are calculated using a CNN. The
vectors are mean pooled and used as features in a feed-forward network. This
architecture is usually less accurate than the ensemble, but runs faster.
| Name | Type | Description |
| ------------------- | ------------------------------------------ | --------------------------------------------------------------- |
| `exclusive_classes` | bool | Whether or not categories are mutually exclusive. |
| `tok2vec` | [`Model`](https://thinc.ai/docs/api-model) | The [`tok2vec`](#tok2vec) layer of the model. |
| `nO` | int | Output dimension, determined by the number of different labels. |
If the `nO` dimension is not set, the TextCategorizer component will set it when
`begin_training` is called.
### spacy.TextCatBOW.v1 {#TextCatBOW}
### spacy.TextCatCNN.v1 {#TextCatCNN}
An ngram "bag-of-words" model. This architecture should run much faster than the
others, but may not be as accurate, especially if texts are short.
> #### Example Config
>
> ```ini
> [model]
> @architectures = "spacy.TextCatBOW.v1"
> exclusive_classes = false
> ngram_size: 1
> no_output_layer: false
> nO = null
> ```
| Name | Type | Description |
| ------------------- | ----- | ------------------------------------------------------------------------------------------------------------------------------------------- |
| `exclusive_classes` | bool | Whether or not categories are mutually exclusive. |
| `ngram_size` | int | Determines the maximum length of the n-grams in the BOW model. For instance, `ngram_size=3`would give unigram, trigram and bigram features. |
| `no_output_layer` | float | Whether or not to add an output layer to the model (`Softmax` activation if `exclusive_classes=True`, else `Logistic`. |
| `nO` | int | Output dimension, determined by the number of different labels. |
If the `nO` dimension is not set, the TextCategorizer component will set it when
`begin_training` is called.
### spacy.TextCatLowData.v1 {#TextCatLowData}
@ -210,17 +312,18 @@ If the `nO` dimension is not set, the Entity Linking component will set it when
### spacy.EmptyKB.v1 {#EmptyKB}
A function that creates a default, empty Knowledge Base from a [`Vocab`](/api/vocab) instance.
A function that creates a default, empty Knowledge Base from a
[`Vocab`](/api/vocab) instance.
| Name | Type | Description |
| ---------------------- | ---- | -------------------------------------------------------- |
| ---------------------- | ---- | ------------------------------------------------------------------------- |
| `entity_vector_length` | int | The length of the vectors encoding each entity in the KB - 64 by default. |
### spacy.CandidateGenerator.v1 {#CandidateGenerator}
A function that takes as input a [`KnowledgeBase`](/api/kb) and a [`Span`](/api/span) object denoting a
named entity, and returns a list of plausible
[`Candidate` objects](/api/kb/#candidate_init).
A function that takes as input a [`KnowledgeBase`](/api/kb) and a
[`Span`](/api/span) object denoting a named entity, and returns a list of
plausible [`Candidate` objects](/api/kb/#candidate_init).
The default `CandidateGenerator` simply uses the text of a mention to find its
potential aliases in the Knowledgebase. Note that this function is