Github now allows you to tag your repositories
It calls it topics
and increases discoveravility of your repositories.

Today I came with a surprise when I entered to a repository of mine. A new option allowed me to add topics
to the repository.

If you press Add topics
, Github lets you to add any number of “tags” to better describe your repository.

Of course, you can then edit (manage)those topics whenever you want.
I expect that to be a really useful feature.