doc bug: Installing-on-Ubuntu...

[CarlFK]

https://github.com/arut/nginx-rtmp-module/wiki/Installing-on-Ubuntu-using-PPAs

sudo apt-get source nginx
cd /usr/src/nginx
-bash: cd: /usr/src/nginx: No such file or directory

apt-get source nginx puts the source in the current dir, in this case nginx-1.18.0/

also, you don't need sudo apt-get source as it is not installing anything into the system.

[CarlFK]

also, there is no PPA in these instructions