Blocks coding guide

I spent some time making a blocks coding guide. Its basically shameless
self-promotion of my next branch work. However, I think it will be
genuinely useful to many gnuradio noobs. It walks you through io
signatures and various block types, work function, with c++ and python
examples. Perhaps others will volunteer to fill in some missing details:


As always, good job. Do you ever sleep :wink:

Cheers & happy hacking,