Allow to set 'Description' in AWS Lambda using Chalice

This is something that I'd like to see if possible.

[Source](https://stackoverflow.com/questions/52686410/how-to-set-description-in-aws-lambda-using-chalice)

Edit: loving this tool btw

Start with the linked Stack Overflow source to understand the requested AWS Lambda behavior, then trace Chalice's Lambda deployment configuration and description-related options. No repository files or tests are named; done means the issue's requested way to set a Lambda description is supported and covered by appropriate tests.

Written by the indexing model from the issue text.