Docs for [ci skip] et al

[CJ-Wright]

It might be nice to have docs on the commit message based CI skipping (and maybe a discussion about it's being temperamental?

[jakirkham]

Also issue ( conda-forge/staged-recipes#1148 ) is relevant. Note that it is a non-actionable issue just tracking this info. Would be happy to close it and have that content absorbed into a doc section somewhere instead.

[jaimergp]

This can be closed. See #2297.