This commit creates docs/rtfm/gem-graph.texi, which from now on will be the
Gem-graph manual source code.
Its first text includes just an introduction, the beginning of a chapter namely
"Gem-graph by example" and a first cross-reference to the section "Hello world".
Doxygen is used to generate documentation, this commit makes sure it is
loaded in the `guix shell` environment (which is useful for guix users).
Signed-off-by: Adrien 'neox' Bourmault <neox@a-lec.org>
Adrien Bourmault
Jean Sirmai