Doc:Install or build>Build>Unix>Run a first simulation: Update the instruction to install BornAgain Python package

Doc:Python scripting>Plot and export>Matplotlib configuration: Improve the section on `Environment variables`

Doc:Python scripting>Plot and export>Matplotlib configuration: Update links to Matplotlib documentation

Doc:Install or build>Build>Unix>Install third-party software: Add instructions to install Qt via command line

`collapse` block does not work as expected.

`collapse` block does not work as expected.

`collapse` block does not work as expected.

Merging branch 'rmdebmsg'  into 'main'.

See merge request !895

Merging branch 'axes7'  into 'main'.

See merge request !893

Merging branch 'axes6'  into 'main'.

See merge request !892

Merging branch 'axes5'  into 'main'.

See merge request !891