This is useful for troubleshooting performance issues that can't be
solved with the GDScript profiler.
The profilers covered aren't the most powerful ones, but they are quick
to set up and understand for occasional users.
This removes the link to the KDevelop setup video tutorial as it's
now outdated.
IDE screenshots were also optimized losslessly using
`oxipng -o6 --strip --zopfli`.
See #3485.
Also added some screenshots fort the "Importing the project" section
Since I was doing these changes I updated also the following:
- added images for the build and run steps for Qt Creator (also changed
one line to match the screenshot taken on Linux in this case)
- fixed typo It's called "Qt Creator" not "QtCreator" althought packages
and launchers sometimes call it like that (I tend to make that mistake
too).
