docs: creates an initial SECURITY.md policy

Signed-off-by: Jennifer Power <[email protected]>

SECURITY.md

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+# OSCAL Compass Security Policy
+
+This policy describes OSCAL Compass security and disclosure information.
+
+## Reporting a vulnerability
+
+To report a vulnerability, either:
+
+1. Report it on Github directly you can follow the procedure described
+   [here](https://docs.github.com/en/code-security/security-advisories/guidance-on-reporting-and-writing/privately-reporting-a-security-vulnerability)
+   and:
+
+    - Navigate to the security tab (e.g. `trestle` [security tab](https://github.com/oscal-compass/compliance-trestle/security)) on the repository
+    - Click on 'Advisories'
+    - Click on 'Report a vulnerability'
+    - Detail the issue, see below for some examples of info that might be
+      useful including.
+
+2. Send an email to `[email protected]` detailing the issue and impacted project(s).
+
+## Public Disclosure
+
+Vulnerabilities once fixed will be shared publicly as a Github [security
+advisory](https://docs.github.com/en/code-security/security-advisories/repository-security-advisories/about-repository-security-advisories)
+and mentioned in the fixed versions' release notes.
+
+## Supported Versions
+
+All OSCAL Compass projects follow [Semantic Versioning](https://semver.org/) terminology and are expressed as x.y.z:
+- where x is the major version
+- y is the minor version
+- and z is the patch version
+
+Security fixes are typically addressed in the main branch and may be backported to one prior minor release depending on severity and feasibility.
+
+## Acknowledgments
+
+Parts of this policy were adapted from the Crossplane [security policy](https://github.com/crossplane/crossplane/blob/master/SECURITY.md)