Hacktoberfest 2020

Hi all,

like the last years, GitHub and Digital Ocean are doing Hacktoberfest.
To participate, you sign up with your GitHub account, and submit four or
more pull requests against public repositories. Of course, we'd be very
happy if you submit some of them against the GNU Radio repositories!

Please don't think there's a high bar for submitting pull requests. If
you find a typo in the documentation (not the wiki docs, but stuff
that's in the tree), submit a typo-fix as a PR, and boom, that's your
first PR. If there's a compiler warning that annoys you, that might be a
quick second PR.

Of course, if you have bigger changes, we're also happy about those. If
you have *really big* changes, please submit a GREP first -- PRs against
the greps repository also count! Or any other repo. So, you can also fix
typos on our website, for example.

I do have one request though. We have a lot of PRs open already on the
GNU Radio repo, and we're having trouble keeping up with code reviews.
You can help us with code reviews to get PRs merged faster. That said,
merging is not a requirement for PRs to count for Hacktoberfest, and we
appreciate all PRs, even if you don't help with code reviews. It would
just be even more helpful.

Some links:
- Hacktoberfest: https://hacktoberfest.digitalocean.com/
- GNU Radio PR queue: https://github.com/gnuradio/gnuradio/pulls
- Need ideas to fix something? Look here:
https://github.com/gnuradio/gnuradio/issues

Cheers,
Martin