Create a comprehensive example of using Fn context data

[michael-w-williams]

Provide a comprehensive how-to on using your Fn context with a function. The how-to should include the following

• [x] Using a context (Completed here: https://github.com/fnproject/tutorials/issues/203)
  • [x] Step by step example of using a context locally
    • [x] Step by step example of using with Docker Hub
    • [x] Details of where context data is stored (.fn directory)
    • [x] Example of creating your own context.yaml file.
• [ ] Using context data in a Function (See: https://github.com/fnproject/tutorials/issues/204)
  • [ ] Step by step example of adding name/value pairs to your context
  • [ ] Example of of how to access the values from a context object passed to your function

Most of this information is covered someplace in our documentation, but we are currently lacking something that is comprehensive and ties all the steps together. The how-to should set some key/value pairs and then use them in a function.

[michael-w-williams]

The first part is complete with this Issue: https://github.com/fnproject/tutorials/issues/203. See this PR: https://github.com/fnproject/tutorials/pull/202 for the merge info.