Add required docs to README.md

[sdowding-koho]

Describe the PR
There is no mention of the validate tag used for required fields in the docs, so I did my best to add one.

Relation issue
None

Additional context
To help people who come after me!

[codecov-commenter]

Codecov Report

Merging #703 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #703   +/-   ##
=======================================
  Coverage   84.77%   84.77%           
=======================================
  Files           7        7           
  Lines        1859     1859           
=======================================
  Hits         1576     1576           
  Misses        177      177           
  Partials      106      106           

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[sdowding-koho]

anything I can do to help get this merged?

[easonlin404]

@sdowding-koho sorry for the late reply, LGTM.

[easonlin404]

Thanks for your contribution. 👍