Docs update in similar.rst

[harkabeeparolus]

Add link and description for Typer. I think this is an interesting project because the design is similar (but not identical) to argh.

[neithere]

Thanks, haven't heard of it! Looks interesting indeed.

In fact FastAPI was my inspiration for the use of Annotated in Argh redesign, so it's not entirely surprising that @tiangolo also went on to the CLI area :)

I'll need to check if there's any commonality between Typer and modern Argh apart from being typing-driven but it's definitely worth comparing those and also letting people make an informed choice.