Docs website landing page needs a better blurb #453

Our docs (https://python-graphblas.readthedocs.io/en/stable/) currently says this:

python-graphblas is a Pythonic interface to the highly performant SuiteSparse:GraphBLAS library for performing graph analytics in the language of linear algebra.

I think we can make this blurb longer, clearer, and more illustrative (our README may do a better job at this). We should assume this is the first time a reader has seen anything about GraphBLAS.

Thanks @stefanv for pointing this out (this point was probably made somewhere in a pyos review too).

PRs welcome :)

edit: I think it should also point to graphblas-algorithms