Help pages: missing/to be improved

[mlep]

(following #308)
This issue tracks the help pages that are missing or need to be improved (for JabRef 5.x).
Please:

• create/improve the corresponding help pages, and then checked them
• if you find other missing/outdated pages, add them to the list

Missing pages

• Manage keywords (PR Add an help section for the management of keywords #311)
• Edit preamble
• Send as email
• Preview style
• Find and replace
• Customizing Theme/Custom Themes CSS (PR Add new page for Custom Themes [advanced] for 5.2 (dev) #324 #325)

Outdated pages

• Custom import filters
• Export
• EndNote Export Filter
• Entry editor
• Field content selector
• File links

[Siedlerchr]

I would change the semantics of the checkbox.
Only check those that are already done.
so when a page is created we can tick ✅ the box

[mlep]

Semantics reversed!

[Siedlerchr]

I added two things to the list. One is the custom theming (CSS based styling)
And the other page which needs to be improved is the help page for File links. Adding a note that you can use the field markers to customize the file names and folder structure of linked files. (File dir pattern and Filename pattern)

[AtrusRiven]

Created pull request for custom themes (#325).