Project does not specify a license

[d-smith]

The author has presented a lot of important ideas in the Production Ready Serverless course, with the code in this repository showing how to implement them. A lot of this code could be reused in other serverless applications, but the project does not specify a license, which makes it unclear if the code can be reused by others.

Adding a license file to this repository would be helpful for those would would like to reuse code.