Add man page

[glfmn]

It would be nice to autogenerate a man page which not only shows all of the help information but also includes detailed information on how to write glitter formats. That way, typing man glit can be a substitute for coming to the README on this repo.

However, it is unclear at this time how much work is required to generate a man page and how many of the things mentioned here are actually publicly useable:

• cli working group's tracking issue
• ripgrep's man file generation
• previous work on generating man pages

Features I would like include:

• include help information generated from structop
• additional documentation for glitter formats
  • test all example formats in the man page against glitter