Mention the gollum wiki project to avoid confusion

[mralusw]

Amazingly, this repo manages to have the same name and about the same current version (0.5.x) as the well-known gollum wiki (https://github.com/gollum/gollum), yet, of course, completely unrelated purposes.

Perhaps mention that this is not the... other project... somewhere... to avoid confusion.

[arnecls]

Good catch.
I was vaguely aware that another project named gollum exists but never looked it up.
I added a link to the readme in this commit 479cafe