update desc for map in all examples
# What does this PR do?

Closes #11797. I've added the remaining the `desc` for `summarization`, `token-classification,` `translation`, `language-modeling ` and updated `requirements.txt` as well. I wasn't sure what to add in `desc` at some places so I've added `# not sure if it's right` comment there. Please let me know if that description looks good or should I replace it with something else?

## Who can review?
@stas00 @sgugger 