Add cpuid man page

[Mno-hime]

I would be helpful to have cpuid man page.

I created one for the OpenIndiana project based on your README.md: OpenIndiana/oi-userland#4345

The source is cpuid.ronn which can be parsed via ronn to cpuid.1. The latter one can be edited manually as well.

[Mno-hime]

Will you incorporate the cpuid.1 man page from https://github.com/OpenIndiana/oi-userland/blob/oi/hipster/components/sysutils/cpuid/files/cpuid.1? Otherwise you can close this.

[Mno-hime]

@tycho ping?

[tycho]

Feel free to make a PR out of this:

• Add another file to use as the man page source, since the existing README.md isn't in an ideal format for use as a man page.
• Add some new steps in GNUmakefile and meson.build to generate/install a man page. It would need to be an optional step. Perhaps via explicit targets "man" and "install-man" for GNU make, and as a configure-time tool check for Meson? Either way, I certainly don't want to be forced to install the manpage generation tool just because I want to compile cpuid.

[tycho]

Also I've just revamped the Travis build stuff and made it more robust (and build on more modern distribution releases). In whatever change you come up with, please ensure that the doc generation gets tested in .travis/script.sh.