Add link to what-is-a-security-bug to SECURITY.md (#8290)

Seemed like an appropriate place to list such documentation as well.

SECURITY.md

@@ -1,3 +1,11 @@
 # Security Policy
 
-Please refer to the [Bytecode Alliance security policy](https://bytecodealliance.org/security) for details on how to report security issues in Wasmtime, our disclosure policy, and how to receive notifications about security issues.
+Please refer to the [Bytecode Alliance security
+policy](https://bytecodealliance.org/security) for details on how to report
+security issues in Wasmtime, our disclosure policy, and how to receive
+notifications about security issues.
+
+For classification of what is and what isn't a security issue please see our
+[online
+documentation](https://docs.wasmtime.dev/security-what-is-considered-a-security-vulnerability.html)
+on the subject.