This:

* conciliates build instructions into a single source folder for kdesrc-build,
  raw CMake, and in the future Craft: ~/kde/src/project
* in the CMake case, actually install and run the application from the start
  using the well established ~/.local path as --prefix
* because of the above, it is no longer necessary to source the prefix file
* switches some mentions from kde-builder to kdesrc-build that were added
  via a direct commit
* removes unnecessary explanations about CMake

In doing so, the instructions got significantly shorter.