[docs] A reminder on linux doc to use $HOME on PATH

Every now and then non-googlers end up having issues  when running gclient
run hooks because they use ~ to refer to the home directory. This update
mentions that they have to use ${HOME}.

Bug: 811748
Change-Id: I5228698d363fe030ff3825371216eca40fc27ce8
Reviewed-on: https://chromium-review.googlesource.com/916283
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536368}
1 file changed