Document how to install an edge build better

[ainar-g]

I couldn't find a good instruction on how people can follow edge or test a build on the edge channel. That info could help us test changes better. The document should obviously state that edge is an unstable branch, and lots of stuff can go wrong, but I still think it's worth documenting.

[ameshkov]

What's wrong with https://github.com/AdguardTeam/AdGuardHome#test-unstable-versions ?

[ainar-g]

@ameshkov, well, for one I couldn't find it :laughing:. Do we have any sort of guidelines regarding what goes into the README and what, into the Wiki? I personally would rather have a leaner README that also has lots of links to more elaborate articles on the Wiki.

[ameshkov]

No guidelines save for common sense