Major refactor: Build Instructions

[herzenschein]

The previous build and installation instructions were extremely old and broken. I've seen many users confused about how to install it.

This at least provides:

• Installation instructions so people don't immediately build from source
• List of build dependencies (more distros need to be added)
• Build and install as root
• Build and install as user
• Non-make-dependent build instructions
• Minimal debugging tips
• How it is used internally in at least one environment

The list of install packages per distribution can be reduced to simply maliit-framework maliit-keyboard for all distros once openSUSE renames their package, it's planned.

The current home build steps don't quite work, but I'd really like if they do. This is the only blocker making this a Draft. As is, maliit appears in the list of Virtual Keyboards in Plasma, and the widget even appears there. But it does not show up, and it mentions no errors. I'm assuming, without looking at the code, that there's some root related stuff happening that hinders it from running, because the same procedure run as root works fine.

Also, compiled in the home folder, it complains about a missing /usr/share/maliit/keyboard2/sounds/key_tick2_quiet.wav, causing a runtime warning. That sound file weirdly enough never gets generated if you compile as user.

We can leave the home build instructions for a later PR so as not to block this one.

When this is merged, I can make some short PRs to address the build instruction documentation in maliit/framework and maliit/keyboard.

Closes #11