Remove install.txt

/usr/local/bin/Installation_guide: Add a convenience script which opens the installation guide in lynx.

/etc/motd: Provide a message with minimal instructions for connecting to internet and inform about the Installation_guide convenience script.

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This is an alternative to #4 (closed) . It doesn't rely on a package that will always be outdated (since changes to the wiki concerning the official installation medium will only ever be made after an iso is released).