docs: explicitly state no security for this repo (#754)

SECURITY.md

@@ -0,0 +1,30 @@
+# Security Policy
+
+We do not offer any security policy for the contents of this repository.
+
+## No Security Provided
+
+This repository was created as a usability convenience, it is not required to
+use asdf.
+
+This repository is a collection of asdf plugins found online, it is a collaborative
+effort by the community. Repositories linked from here are:
+
+- not covered by any security policy from the asdf team
+- not scanned automatically for dangerous or malicious operation
+
+## What the asdf Team Recommend
+
+The expectation is that users will vet the code of each plugin before use, as is
+expected of other OSS plugin and package ecosystems.
+
+The asdf core team discourage the use of this shortname repository. Read the code
+in the plugins you use. Install the plugins you trust via the direct URL method:
+
+```bash
+asdf plugin add <name> <git_url>
+```
+
+---
+
+For the asdf core Security Policy, see https://github.com/asdf-vm/asdf/blob/master/SECURITY.md