Documentation/email-clients.txt: add some info about gmail

Works.  Use "Insert file..." or external editor.

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Gmail (Web GUI)

If you just have to use Gmail to send patches, it CAN be made to work.  It

requires a bit of external help, though.

The first problem is that Gmail converts tabs to spaces.  This will

totally break your patches.  To prevent this, you have to use a different

editor.  There is a firefox extension called "ViewSourceWith"

(https://addons.mozilla.org/en-US/firefox/addon/394) which allows you to

edit any text box in the editor of your choice.  Configure it to launch

your favorite editor.  When you want to send a patch, use this technique.

Once you have crafted your messsage + patch, save and exit the editor,

which should reload the Gmail edit box.  GMAIL WILL PRESERVE THE TABS.

Hoorah.  Apparently you can cut-n-paste literal tabs, but Gmail will

convert those to spaces upon sending!

The second problem is that Gmail converts tabs to spaces on replies.  If

you reply to a patch, don't expect to be able to apply it as a patch.

The last problem is that Gmail will base64-encode any message that has a

non-ASCII character.  That includes things like European names.  Be aware.

Gmail is not convenient for lkml patches, but CAN be made to work.

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