Update INSTALL

[firoj0]

Thanks for taking the time to contribute to Git! Please be advised that the
Git community does not use github.com for their contributions. Instead, we use
a mailing list ([email protected]) for code submissions, code reviews, and
bug reports. Nevertheless, you can use GitGitGadget (https://gitgitgadget.github.io/)
to conveniently send your Pull Requests commits to our mailing list.

For a single-commit pull request, please leave the pull request description
empty: your commit message itself should describe your changes.

Please read the "guidelines for contributing" linked above!

[github-actions]

Errors and warnings found by git-po-helper in workflow #873:

INFO no missing blobs of po/* in partial clone    
------------------------------------------------------------------------------
WARNING commit c52633f: author (firoj0 <[email protected]>) and committer (GitHub <[email protected]>) are different 
------------------------------------------------------------------------------
ERROR commit c52633f: subject ("Update INSTALL") does not have prefix "l10n:" 
------------------------------------------------------------------------------
ERROR commit c52633f: empty body of the commit message, no s-o-b signature 
INFO checking commits: 0 passed, 1 failed.        
------------------------------------------------------------------------------
INFO downloading pot file from https://github.com/git-l10n/pot-changes/raw/pot/master/po/git.pot 

ERROR: fail to execute "git-po-helper check-commits"