CG: Add comment about git-cl editor (issue 41310043)

[lilyliska]

Reviewers: ,

Message:
Describing the solution for my problem when using git-cl for the first
time

Description:
CG: Add comment about git-cl editor

git-cl fires either the editor specified by the EDITOR environment
variable or vi if EDITOR isn't defined.
Commit mentions this in the CG

Please review this at https://codereview.appspot.com/41310043/

Affected files (+5, -0 lines):
  M Documentation/contributor/source-code.itexi


Index: Documentation/contributor/source-code.itexi
diff --git a/Documentation/contributor/source-code.itexi  
b/Documentation/contributor/source-code.itexi
index  
f44dd31b3fd2534a0fe591ab10014e9184e51e93..6af2b6fbfe897b466ada93ad0912c5b48d1118a9  
100644
--- a/Documentation/contributor/source-code.itexi
+++ b/Documentation/contributor/source-code.itexi
@@ -1384,6 +1384,11 @@ can be used.

 @end itemize

+First you will see a terminal editor where you can edit the
+message that will accompany your patch. @code{git-cl} will respect
+the @var{EDITOR} environment variable if defined, otherwise it
+will use @code{vi} as the default editor.
+
 After prompting for your Google email address and password, the
 patch set will be posted to Rietveld, and you will be given a URL
 for your patch.