Changes to contribution guidelines

[Martin Braun]

Hi all,

before we finish this year, we do want to announce one more change in
how we accept contributions into the GNU Radio code base.

One thing that we take very seriously is the whole business of license
compliance. GNU Radio is GPLv3-licensed, and that's not going to change.
But also, we have to make sure that code upstreamed is legally OK to go
into our branches (that usually means it's not copyrighted elsewhere,
etc.). Since we can't do a thorough check for every submission (even if
we wanted to, we don't know and can't know the origin of all the code),
we put the burden onto the developer. So far, they agree to this by
signing the CLA that so many of you have signed.

The CLA signing process has been criticized as being overly complex and
a barrier for entry to contributing to GNU Radio. We agree with this
statement.

Moving forward, we will no longer require users to have a CLA filed.
Instead, we will require signing a DCO (Developer's Certificate of
Origin). You can do that by using the `git commit -s` command line
argument. Our updated contributing guide has more details
(https://github.com/gnuradio/gnuradio/blob/master/CONTRIBUTING.md#dco-signed).

Since there is no copyright assignment in the DCO, this means that new
components of GNU Radio can be upstreamed without copyright assignment.
The copyright remains with the author or their company.

We hope this means that new contributors are more likely to upstream
their code to GNU Radio, while existing contributors hopefully won't be
upset by amending '-s' to their git commits.

We're happy to discuss this change, but I suggest reading a blog article
by Bradley Kuhn on the subject (Bradley is unrelated to GNU Radio, but
this particular article happens to also express the opinions of the GNU
Radio leadership):
https://sfconservancy.org/blog/2014/jun/09/do-not-need-cla/

Maybe this will motivate folks to do some Christmas hacking!

Cheers,
Martin