Improve docs [ci skip]

Signed-off-by: Paolo Di Tommaso <[email protected]>

docs/plugins.md

@@ -365,7 +365,7 @@ You can also use a different plugin registry with the `NXF_PLUGINS_TEST_REPOSITO
 For example:
 
 ```bash
-# custom registry at https://github.com/my-org/plugins
+# custom plugin repository at https://github.com/my-org/plugins
 export NXF_PLUGINS_TEST_REPOSITORY="https://raw.githubusercontent.com/my-org/plugins/main/plugins.json"
 
 # custom plugin release
@@ -374,6 +374,11 @@ export NXF_PLUGINS_TEST_REPOSITORY="https://github.com/nextflow-io/nf-hello/rele
 nextflow run <pipeline> -plugins nf-hello
 ```
 
+:::{tip}
+This variable can be either the URI of a plugins repository JSON file or the URI of a specific plugin JSON meta file.
+In the latter case it should match the pattern `https://host.name/some/path/<plugin id>-X.Y.Z-meta.json`.
+:::
+
 ## Offline usage
 
 To use Nextflow plugins in an offline environment: