Add a glossary

[alice-i-cecile]

Key terms:

• pane
• workspace
• gizmo (bevy_gizmos sense)
• gizmo (transform gizmo sense, needs a new word)
• tool
• toolbar
• command palette
• dropdown menu
• plugin (bevy_app::Plugin sense)
• extension (things end users can add to the editor)

[n1ght-hunter]

do we want to add menu here as well?

[alice-i-cecile]

I think "drop down menu" is probably better :)