talkatu/talkatu

Add a minimum version to cmark

2021-03-14, Gary Kramlich
7dabf1ebead0
Add a minimum version to cmark

The pc file doesn't exist in versions earlier than this, but this should help
people who have version 0.26.0 of cmark to realize they need a newer version.

Testing Done:
Ran locally.

Reviewed at https://reviews.imfreedom.org/r/571/
Talkatu is versioned in [mercurial](https://www.mercurial-scm.org/) and is
available on [keep.imfreedom.org](https://keep.imfreedom.org/talkatu/talkatu).
All contributions are provided via review requests at [reviews.imfreedom.org](https://reviews.imfreedom.org/).