Create SECURITY.md (GeoNode#10285)

* Create SECURITY.md

* Update SECURITY.md

fix minor typo

Co-authored-by: Florian Hoedt <gannebamm@gmail.com>

Author: afabiani

SECURITY.md

@@ -0,0 +1,17 @@
+# Security Policy
+
+## Supported Versions
+
+GeoNode versions supported with security updates.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 4.0.x   | :white_check_mark: |
+| < 4.0   | :x:                |
+
+## Reporting a Vulnerability
+
+- **DO NOT** send a security alert on the public mailing list or any other public channel
+- **SEND** the report to geonode-psc@lists.osgeo.org and be prapred to collaborate with the GeoNode PSC
+
+Thanks for you support and help!