better describe linkage with git-evtag

This is now basically a JS reimplementation, right? In that case, can we make that clearer, and link to git-evtag a bit more prominently in the intro?

Calling this `git-evtag-js` might be clearer for example. And given that I think no one would really feel a need to parallel install them, why not just take the `git evtag` name, i.e. install the binary as `/usr/bin/git-evtag`.

I'm happy to cross link from git-evtag (which is now the C, Python, and Rust implementation) too.

Review the project introduction and the current installation name, then compare the wording with git-evtag’s description. Done should clearly explain the JavaScript relationship, link to git-evtag prominently, and settle the proposed project and binary naming.

Written by the indexing model from the issue text.