DOC: fix "needed" typo

While at it use "You" instead of "They" as in the context
it seems to make more sense to refer to "you", as it is
you that are going to be running the command, there is no
"they".

Signed-off-by: Thiago Farina <tfarina@chromium.org>
(cherry picked from commit 9f72a39f68247893bfb1806f5198cd22f1580809)
(cherry picked from commit b9b85d488a201ce7a2c32c1fad4eab7c745618f3)
diff --git a/CONTRIBUTING b/CONTRIBUTING
index 0f6b9ed..968da4f 100644
--- a/CONTRIBUTING
+++ b/CONTRIBUTING
@@ -626,14 +626,14 @@
    $ git show master..
 
 And once you're satisfied, you should update your master branch to be sure that
-nothing changed during your work (only neede if you left it unattended for days
+nothing changed during your work (only needed if you left it unattended for days
 or weeks) :
 
    $ git checkout -b 20150920-fix-stats-rebased
    $ git fetch origin master:master
    $ git rebase master
 
-They can build a list of patches ready for submission like this :
+You can build a list of patches ready for submission like this :
 
    $ git format-patch master