merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/Documentation/git-citool.txt

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+git-citool(1)
+=============
+
+NAME
+----
+git-citool - Graphical alternative to git-commit
+
+SYNOPSIS
+--------
+[verse]
+'git citool'
+
+DESCRIPTION
+-----------
+A Tcl/Tk based graphical interface to review modified files, stage
+them into the index, enter a commit message and record the new
+commit onto the current branch.  This interface is an alternative
+to the less interactive 'git commit' program.
+
+'git citool' is actually a standard alias for `git gui citool`.
+See linkgit:git-gui[1] for more details.
+
+GIT
+---
+Part of the linkgit:git[1] suite