docs: reorganize the About section (#18236)

As part of an information architecture overhaul, this PR reorganizes the
About section and adds a Support section (but not content to it yet)

[preview](https://coder.com/docs/@docs-ia-about/about)

this PR is intentionally limited in scope so that we can ship meaningful
changes faster and followup PRs should include:

- [ ] edit + overhaul the About page
- [ ] decide on the `start` directory
- [ ] ~screenshots page updates~ (this should happen July or later)

redirects PR: https://github.com/coder/coder.com/pull/944

---------

Co-authored-by: EdwardAngert <17991901+EdwardAngert@users.noreply.github.com>

docs/about/contributing/SECURITY.md

@@ -0,0 +1,11 @@
+# Security Policy
+
+Coder welcomes feedback from security researchers and the general public to help improve our security.
+If you believe you have discovered a vulnerability, privacy issue, exposed data, or other security issues
+in any of our assets, we want to hear from you.
+
+If you find a vulnerability, **DO NOT FILE AN ISSUE**.
+Instead, send an email to
+<security@coder.com>.
+
+Refer to the [Security policy](https://coder.com/security/policy) for more information.