Include `injectable` in library comparison

**Is your feature request related to a problem? Please describe.**
I just found about this small library [injectable](https://github.com/roo-oliv/injectable) that seems to achieve a similar effect to Hamilton.

**Describe the solution you'd like**
Include this in the docs so other people can know about it.

**Describe alternatives you've considered**
I guess this is totally optional.

**Additional context**
It has a pretty different style; the overlap might not be that big.