Add extra warning to "Installing add-ons" section of User Guide

[Qchristensen]

Following discussion on #16486, the purpose of this PR is to add more warning / ways of verifying add-ons to the add-on section of the User Guide. This can then be referred to from the quick start guide changed proposed in #16486.

Link to issue number:

Summary of the issue:

Intention is to expand on the warning of the risks of add-ons mentioned in the user guide, and offer some suggestions for users to reassure themselves about the author of add-ons prior to installing.

(It should perhaps also be noted, there is no new or additional risk with add-ons than there ever has been. We just want to be sure users are aware of what add-ons are and can do before installing them).

Description of user facing changes

Update user guide with additional paragraph of information.

Description of development approach

Testing strategy:

Known issues with pull request:

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.

[Adriani90]

@Qchristensen please also see #16316.

[Qchristensen]

Suggested change

	Add-ons are scanned by [Virus Total](https://www.virustotal.com/), however, this only detects known malware at submission time.

[seanbudd]

did you want to commit this somewhere?

[seanbudd]

I think it would be better to part of the previous paragraph

[Qchristensen]

I initially had it at the end of that paragraph, but just reading it again as a whole:

"Just because an add-on is available in the NVDA Add-on Store, does not mean that it has been approved or vetted by NV Access or anyone else. It is very important to only install add-ons from sources you trust. The functionality of add-ons is unrestricted inside NVDA. This could include accessing your personal data or even the entire system."

Perhaps between "... approved or vetted by NV Access or anyone else." and "It is very important to only install add-ons from sources you trust..." would be better?

[seanbudd]

that makes sense to me