Add security section - WIP.
Added sections 'Involving the Security Team' and 'X-Frame-Options'
fixed minor issues with the CSP section and rewrote the bullet points to a field list
Finished CSP section and added projects simplifying the use of CSP.
Using local copy of security.
Restore freddyb's changes.
Fix comma, adjust wording.
Clarify position on presentational classes
Clarify two-space indenting in HTML templates
Major text-shortening to make it more relevant to Mozillians.
update with current VPN information

The MPT VPN has been deprecated in favour of the Mozilla VPN, and will eventually be turned off entirely (likely in the not-too-distant future).
Merge pull request #38 from phrawzty/patch-1

update with current VPN information
Fix broken Pro Git url
Merge pull request #39 from vtsatskin/patch-1

Fix broken Pro Git url
Use consistent two newline style
Use "element" not "elmt"
Don't say not to use CSP
Simplify wording
Merge branch 'qll/csp-and-security'
some indenting ideas