docs: Installation on ChromeOS

[Karl Berry]

    install on ChromeOS
    ...
    Android: https://williewong.wordpress.com/2017/06/30/texlive-on-android/
                   https://wiki.termux.com/wiki/TeX_Live
    iOS: https://gamma-level.com/iphoneos/ports/texlive

Thanks. I made links on https://tug.org/texlive/quickinstall.html.
I slightly reformatted your https://tug.org/texlive/chromeos/ page (and
linked to the basic instructions instead of duplicating them).

    somehow, the installation on ChromeOS is more important than the
    Cygwin, because there is a native alternative in Windows, but not on
    Chrome.

I don't think the order in this short list is significant.
Since Cygwin info has been around a lot longer than Chrome has existed,
I didn't change it.

    The information on Android will be short-lived because Google is in
    the process of merging it with ChromeOS.

Please (anyone) let me know when updates to any of these items are
necessary.  It's not something I'll notice myself. --thanks, karl.