Unit Test Policy

[robmoffat]

Minor Issue

We now have the OpenSSF badge on the README. It's at 99%. To get to 100%, we need a test policy for the FDC3 unit tests. It could be something written down like:

Any change to the FDC3 specification typescript codebase must be supported by accompanying unit tests

or a rule in our build system that says the build fails unless the coverage increases / stays same from the previous build.

[kriswest]

@robmoffat uses https://about.codecov.io/ for spring bot's code coverage (free for opensource)

[ashok-hariharan]

Wish if I could take this as my first contribution to opensource