add library manager documentation

[jperedadnr]

Issue

Fixes #713

Progress

• Change must not contain extraneous whitespace
• License header year is updated, if required
• The PR name must follow the pre-defined format
• Verify the contributor has signed Gluon Individual Contributor License Agreement (CLA)

[Oliver-Loeffler]

This looks as a great starting point to me. Also we can add more docs here at this space. On which OS did you create the screenshots?

[jperedadnr]

The idea is to have docs for every other documentation that we want to include, of course. For now, this is a first contribution, for the Library Manager feature, that is not included elsewhere (except from the Gluon docs).

I'm on macOS.

[Oliver-Loeffler]

@jperedadnr Do you have any chance to preview the MD on Linux or Windows? The images created on macOS usually appear twice as large as needed due to hidpi rendering on macOS. However, for all images which only show a small portion of the screen, scaling can be set to 50%. Not sure how this is handled between macOS / Windows and Linux. On Windows the images appear too large. Is there any chance to assign dpis to an image tag?

[jperedadnr]

I was trying to limit the size via css, but I noticed that doesn't work with GitHub md files, so I've finally added the old width="400" to the img tag. Did you check after my latest commit?

[Oliver-Loeffler]

This seems now to work quite fine. 400px seems reasonable for the most elements. For images like SceneBuilder01.png I would go with 800px or 600px, everything else 400px is okay. However, this is my subjective impression. Technically this is fine.

[Oliver-Loeffler]

Looks now quite nice.