git-node: improve instructions logs when manual amending is required

[juanarbol]

I had to manually change the commit message in one PR, and totally forgot to continue the landing process with git node land --continue this may be helpful for new collaborators.

[codecov]

Codecov Report

Merging #560 (1b65aaa) into main (e9bb948) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #560   +/-   ##
=======================================
  Coverage   82.57%   82.57%           
=======================================
  Files          35       35           
  Lines        1750     1750           
=======================================
  Hits         1445     1445           
  Misses        305      305           

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