* Remove the build instructions because they are not end user relevant
and belong into Qt Creator's README.md.
* Restructure into the sections "About ...", "Activating ..." and
"Configuring ...".
* Simplify/clarify here and there.
Change-Id: I7b3abd03bc4fe9215db804a4cd69e9d796b8bf9b
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>