Fixed spelling in SECURITY.md

[pointydev]

Changes the spelling of a word in SECURITY.md

Description

Changes nessesary to necessary

Motivation and Context

I spotted a spelling error and fixed it

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.

[geominorai]

Might as well fix the spelling for separate and the comma splices too while you are at it:

Don't use the root MySQL user with SourceBans; make a separate SQL account
Trust your Admins, but don't
I found a security hole. What do I do?
Open an issue on the GitHub repo with all necessary info.