ci: add some documentation in the workflow files

.github/workflows/audit.yml

@@ -1,3 +1,5 @@
+# A routine check to see if there are any Rust-specific security vulnerabilities in the repo we should be aware of.
+
 name: audit
 on:
   workflow_dispatch:

.github/workflows/post-release.yml

@@ -1,4 +1,4 @@
-# Actions to run after releasing a version.
+# Actions to run after releasing a version, like generating documentation via mkdocs or notifying packaging repos.
 name: post-release
 
 on: