PTL-1341: improve FUI docs - entity management

[wjhendry]

Thank you for contributing to the documentation.

Do the changes you have made apply to both Current and Previous versions?
CURRENT ONLY

Have you checked all new or changed links?
NOT YET

Is there anything else you would like us to know?
NO

For reference:

• We have an internal contributions guide
• We have a style guide

This week's exciting excerpts from the style guide

• We write in UK English, with Oxford English Dictionary (OED) spellings, grammar and vocabulary.

Use the present tense wherever possible. Only use another tense where it is strictly necessary.

• Present tense (preferred whenever possible): The script creates a new folder.
• Future tense (avoid whenever possible): The script will create a new folder.