fix typos in desc and docs

docs/source/index.rst

@@ -12,7 +12,7 @@
 
 **TextBrewer** is a PyTorch-based model distillation toolkit for natural language processing.
 
-It includes various distillation techniques from both NLP and CV, and provides an easy-to-use distillation framework, which allows users to quickly experiment with state-of-the-art distillation methods to compress the model with a relatively small sacrifice in performance, increase the inference speed and reduce the memory usage.
+It includes various distillation techniques from both NLP and CV field and provides an easy-to-use distillation framework, which allows users to quickly experiment with the state-of-the-art distillation methods to compress the model with a relatively small sacrifice in the performance, increasing the inference speed and reducing the memory usage.
 
 Main features
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