README.md: update required for API change

[bchretien]

The "Getting Started" section of the README currently indicates:

" Create a new binary directory for your clean project.
:CMakeCreateProject <build-dir-name>

But this part of the API was apparently changed in the last release to CMakeCreateBuild. Since there may be other notes to add regarding the last release, I guess you're the best suited for this update ;-)

[jalcine]

Good catch, @bchretien. I'll make the patch for this now, but I think I might just end up documentating the entire API built by cmake-vim and for the next fitting minor release, push the more complete documentation out.

[jalcine]

Going to leave this open until I finish documentating the codebase.

[jalcine]

Blocks #50.