I just registered here, because I want to tell people how to install latest release on a RPI 3. Any suggestion where I can post a guide?
You should ask a question on regular Monero SE for how to set up a RPi3 for monero, and then answer your own question with a detailed how-to (as Jun Li recommended in the comment).
There are build instructions on the Monero GitHub main page: https://github.com/monero-project/monero
My advice would be to edit that README.md if the instructions aren't correct.
If you mean how to just use the binaries, that's no different than for any brand of Linux, so probably shouldn't have it's own post.