Add note about webgl player memory

[caseyyee]

as per SECVRITY article.

[caseyyee]

Just as a added note. Had troubles with the player set to 1024+MB memory using Chromium VR. Worked fine using Firefox. Could be because Chromium VR builds are 32bit? Ended up going with 768MB which works in both browsers just fine.

Now that @toji has 64bit builds available of Chromium, we should try it out to find out.