docs: add recommendation of pull request breakdown to contributing guides

[danielleadams]

Description of changes

Adds more guidance on opening a pull request so that it's easier for CLI team members to review:

1. Recommends breaking down pull requests greater than 12 files changed.
2. Recommends making an initial pull request with linting changes.

Checklist

• PR description included
• yarn test passes

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #11412 (01135ac) into dev (6e02691) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev   #11412   +/-   ##
=======================================
  Coverage   49.45%   49.45%           
=======================================
  Files         692      692           
  Lines       33424    33424           
  Branches     6840     6840           
=======================================
+ Hits        16529    16530    +1     
+ Misses      15370    15369    -1     
  Partials     1525     1525           

Impacted Files	Coverage Δ
...li/src/domain/amplify-usageData/getUsageDataUrl.ts	100.00% <0.00%> (+12.50%)	⬆️

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