Update the README and related files.

This commit generally updates some language in the "About" section, and other sections with respect to keeping accurate information, and laying out the project goals in a clear way.

We're also marking Alacritty as "beta" software at this point, not that this has any explicit meaning.

This bumps the version number to 0.2.5 and prepares everything for the
next versioned release.

This commit removes the boilerplate comments that come with the template snapcraft.yaml. It also expand the description to match the project's README.

Since the version 0.2.2 had some significant breakage which affects a
large number of users, this 0.2.3 release aims at providing a stable
release which works for everyone without any major regressions.