Add license information to model cards (#3864)

Close #3357

model_cards/albert-base-v1-README.md

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 tags:
 - exbert
+
+license: apache-2.0
 ---
 
 <a href="https://huggingface.co/exbert/?model=albert-base-v1">

model_cards/albert-xxlarge-v2-README.md

 ---
 tags:
 - exbert
+
+license: apache-2.0
 ---
 
 <a href="https://huggingface.co/exbert/?model=albert-xxlarge-v2">

model_cards/bert-base-cased-README.md

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 tags:
 - exbert
+
+license: apache-2.0
 ---
 
 <a href="https://huggingface.co/exbert/?model=bert-base-cased">

model_cards/bert-base-chinese-README.md

+---
+language: chinese
+---

model_cards/bert-base-german-dbmdz-cased-README.md

+---
+language: german
+license: mit
+---

model_cards/bert-base-german-dbmdz-uncased-README.md

+---
+language: german
+license: mit
+---

model_cards/bert-base-multilingual-cased-README.md

+---
+language: multilingual
+
+license: apache-2.0
+---

model_cards/bert-base-multilingual-uncased-README.md

+---
+language: multilingual
+
+license: apache-2.0
+---

model_cards/bert-base-uncased-README.md

 ---
 tags:
 - exbert
+
+license: apache-2.0
 ---
 
 <a href="https://huggingface.co/exbert/?model=bert-base-uncased">

model_cards/bert-large-cased-README.md

+---
+license: apache-2.0
+---

model_cards/camembert-base-README.md

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 language: french
+
+license: mit
 ---
 
 # CamemBERT: a Tasty French Language Model

model_cards/distilbert-base-multilingual-cased-README.md

+---
+language: multilingual
+license: apache-2.0
+---

model_cards/distilbert-base-uncased-README.md

 ---
 tags:
 - exbert
+
+license: apache-2.0
 ---
 
 <a href="https://huggingface.co/exbert/?model=distilbert-base-uncased">

model_cards/distilgpt2-README.md

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 tags:
 - exbert
+
+license: apache-2.0
 ---
 
 <a href="https://huggingface.co/exbert/?model=distilgpt2">

model_cards/distilroberta-base-README.md

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 tags:
 - exbert
+
+license: apache-2.0
 ---
 
 <a href="https://huggingface.co/exbert/?model=distilroberta-base">

model_cards/google/electra-base-discriminator/README.md

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 language: english
 thumbnail: https://huggingface.co/front/thumbnails/google.png
+
+license: apache-2.0
 ---
 
 ## ELECTRA: Pre-training Text Encoders as Discriminators Rather Than Generators

model_cards/google/electra-base-generator/README.md

 ---
 language: english
 thumbnail: https://huggingface.co/front/thumbnails/google.png
+
+license: apache-2.0
 ---
 
 ## ELECTRA: Pre-training Text Encoders as Discriminators Rather Than Generators

model_cards/google/electra-large-discriminator/README.md

 ---
 language: english
 thumbnail: https://huggingface.co/front/thumbnails/google.png
+
+license: apache-2.0
 ---
 
 ## ELECTRA: Pre-training Text Encoders as Discriminators Rather Than Generators

model_cards/google/electra-large-generator/README.md

 ---
 language: english
 thumbnail: https://huggingface.co/front/thumbnails/google.png
+
+license: apache-2.0
 ---
 
 ## ELECTRA: Pre-training Text Encoders as Discriminators Rather Than Generators

model_cards/google/electra-small-discriminator/README.md

 ---
 language: english
 thumbnail: https://huggingface.co/front/thumbnails/google.png
+
+license: apache-2.0
 ---
 
 ## ELECTRA: Pre-training Text Encoders as Discriminators Rather Than Generators