Add pandarallel to ecosystem documentation
As proposed by datapythonista here: https://github.com/nalepae/pandarallel/issues/28

@nalepae is this this active? Mind merging master the CI issues should now be fixed. @alimcmaster1: Yes this PR (and `pandarallel` itself) are both active.

I'll be happy to be part of the `pandas` ecosystem!

 Thanks @nalepae 