upd(rr.yaml): Add comment to the rpc section

[tarampampam]

Closes https://github.com/spiral/roadrunner/issues/619

PR Checklist

• [x] All commits in this PR are signed (git commit -s).
• [x] The reason for this PR is clearly provided (issue no. or explanation).
• [ ] The description of changes is clear and encompassing.
• [ ] Any required documentation changes (code and docs) are included in this PR.
• [ ] Any user-facing changes are mentioned in CHANGELOG.md.
• [ ] All added/changed functionality is tested.

[codecov[bot]]

Codecov Report

Merging #32 (c2d6359) into master (c4e1797) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #32   +/-   ##
=======================================
  Coverage   52.20%   52.20%           
=======================================
  Files          11       11           
  Lines         295      295           
=======================================
  Hits          154      154           
  Misses        131      131           
  Partials       10       10           

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