doc: update docker readme

docker/README.md

@@ -3,9 +3,23 @@
 - latest
 - 0.4
 
-# vnetod
+# vnetod*
 
-Dotenv state switcher
+<small><strong>*</strong> inverted word "dotenv"</small>
+
+Are you still switching sections in your dotenv file manually? Try this dotenv
+section switcher!
+
+You can create many sections in your `.env` and switch between them.
+
+Rules:
+
+- Section name starts on a new line with `###` symbols (Ex. `### local`)
+- Section can contain multiple comma-separated names (Ex.
+  `### local,staging`)
+- Each section name may specify a namespace (Ex. `### debug:on,dev:on`). If a
+  section doesn't contain a namespace, it's a global namespace.
+- Section ends if line is empty or contains a new section name.
 
 # Usage