feat: add usageDescription option for darwin/mas targets

[malept]

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:

Adds a convenience option to set usage descriptions for the macOS store, on darwin/mas targets.

Reference: electron/electron#19871 (review)

[codecov-io]

Codecov Report

Merging #1049 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1049      +/-   ##
==========================================
+ Coverage   99.42%   99.42%   +<.01%     
==========================================
  Files          14       14              
  Lines         695      699       +4     
==========================================
+ Hits          691      695       +4     
  Misses          4        4

Impacted Files	Coverage Δ
src/mac.js	100% <100%> (ø)	⬆️

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