templates/about: mention that "dependencies" isn't implemented yet

Adding a comment that the `dependencies` key in the `package.metadata.docs.rs` key isn't yet used for builds should clear up some confusion.

Author: decathorpe

templates/about.hbs

@@ -117,6 +117,7 @@ no-default-features = true
 default-target = "x86_64-unknown-linux-gnu"
 rustc-args = [ "--example-rustc-arg" ]
 rustdoc-args = [ "--example-rustdoc-arg" ]
+# the dependencies key is not being used for builds yet
 dependencies = [ "example-system-dependency" ]</pre></code>
 
   <h4>Version</h4>