[nasa/cryptolib#222] Initial set of requirements in markdown

[jlucas9]

Initial set of requirements in markdown format. Will need to add traceability to unit tests in next round as well as expand into SDLS-EP PICs.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.50%. Comparing base (e68419b) to head (a5974fa).
Report is 2 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #263   +/-   ##
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  Coverage   82.50%   82.50%           
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  Files          40       40           
  Lines       10052    10052           
  Branches      821      821           
=======================================
  Hits         8293     8293           
  Misses       1460     1460           
  Partials      299      299           

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