[Feature Request] Add install instructions

[strk]

The README file only documents how to install in a development environment, but not how to install systemwide.
Such documentation would have been useful for me to write an 'install' make target (see #433 ) and maybe to also give me an idea why it wasn't provided (maybe there are so many option that's hard to pick one?)

[ihabunek]

It's documented in the docs:

• rendered: https://toot.bezdomni.net/installation.html
• source: https://github.com/ihabunek/toot/blob/master/docs/installation.md

[strk]

the GNU Coding Standards suggests an INSTALL file:
https://www.gnu.org/prep/standards/standards.html#Releases

I didn't find a mention of docs/installation.md from the top-level README file, maybe there should be one ?

[strk]

I'm thinking docs for terminal users, not involving use of a browser

[strk]

Also, the docs/installation.md is referring to installing a binary package, while what I mean is install from the source, ie: after downloading the source (package or git clone) and getting OFF the network. Instructions to let you build and install the application on the system in these conditions.