Update doc for {Summarization,Translation}Pipeline and other tweaks

README.md

@@ -538,6 +538,8 @@ You can create `Pipeline` objects for the following down-stream tasks:
  - `text-classification`: Initialize a `TextClassificationPipeline` directly, or see `sentiment-analysis` for an example.
  - `question-answering`: Provided some context and a question refering to the context, it will extract the answer to the question in the context.
  - `fill-mask`: Takes an input sequence containing a masked token (e.g. `<mask>`) and return list of most probable filled sequences, with their probabilities.
+ - `summarization`
+ - `translation_xx_to_yy`
 
 ```python
 from transformers import pipeline