Update README

The README is especially modified to reduce the usage of links that might change in the future.
9 jobs for doc/readme in 29 minutes and 41 seconds (queued for 55 minutes and 15 seconds)
Status Job ID Name Coverage
  Test
passed #41448
clazy

00:01:01

passed #41449
qmllint

00:00:25

 
  Build
passed #41452
archlinux

00:01:02

passed #41451
debian-sid

00:00:52

passed #41450
neon-bionic

00:01:02

 
  Deploy
passed #41455
android

00:14:53

passed #41453
linux-appimage

00:07:20

passed #41456
mac-osxcross

00:01:31

failed #41454
allowed to fail
windows-mxe

00:01:31

 
Name Stage Failure
failed
windows-mxe Deploy
make[2]: *** [CMakeFiles/kaidan.dir/build.make:2734: CMakeFiles/kaidan.dir/src/RegistrationManager.cpp.obj] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [CMakeFiles/Makefile2:68: CMakeFiles/kaidan.dir/all] Error 2
make: *** [Makefile:95: all] Error 2
$ mv build/bin/kaidan.exe kaidan.exe
mv: cannot stat 'build/bin/kaidan.exe': No such file or directory
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1