[documentation] Make gitlab guides more prominent

Think about where the gitlab tutorials should be. They are a bit hidden at the bottom of tools now. Perhaps "git and gitlab" should be their own section so they are really easy to find when people are on-boarding. Could also nest all the pages under "tutorials" then... :)

To Do:

• Move gitlab etc tutorials to its own section (alongside tools)
• Add a gitlab sticker on how page
• Think about whether stuff like "what to include in your repo" should be in the gitlab section rather than analysis. All gitlab mentions in other section should then link back to the main gitlab area.

mentioned in issue #29 (closed)

marked the checklist item Move gitlab etc tutorials to its own section (alongside tools) as completed

marked the checklist item Add a gitlab sticker on how page as completed

now a dedicated gitlab section which references "materials" and "repository" instead of "code" only.

closed

marked the checklist item Think about whether stuff like "what to include in your repo" should be in the gitlab section rather than analysis. All gitlab mentions in other section should then link back to the main gitlab area. as completed