Drop generated manpages when there is an `.rst` source

[b1rger]

It would be great if the build system did the generation of the manpage files instead

[LBCrion]

I originally opted to distribute the docs as both .rst and man pages, in order to avoid introducing a build time dependency on docutils. Perhaps it's worth adding this as an optional dependency? I.e. if docutils are present we rebuild the manpages and if it isn't we use the included version?

[b1rger]

Hm, I was thinking of the overhead of maintaining two files with the same content in the repository - at some point a contributor might not realize that one format depends on the other and only changes stuff in one of the two. But feel free to keep them both and close this issue!

(In the packages I maintain there is usually a build step that builds manpages. That step only runs if the required utility is available - see for example in sway or labwc)

[LBCrion]

I updated meson.build to check if rst2man is available and if it is, the man pages will be rebuilt before installation.