Added link to the csrf template tag in the csrf documentation page

[alexgmin]

Trac ticket number

N/A

Branch description

The CSRF docs, in the 2nd point of how it works mention the csrf template tag but do not link to is.

Checklist

• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period.
• I have checked the "Has patch" ticket flag in the Trac system.
• I have added or updated relevant tests.
• I have added or updated relevant docs, including release notes if applicable.
• I have attached screenshots in both light and dark modes for any UI changes.

[alexgmin]

I have no idea why those 2 db tests failed on a docs only change. I'm also surprised they are ran in doc only changes.

[sarahboyce]

Thank you for this @alexgmin 👍