vdoc: group constants + minor fixes

cmd/v/help/doc.txt

@@ -17,6 +17,8 @@ Options:
   -l              Show the locations of the generated signatures. (For plaintext only)
   -m              Generate docs for modules listed in that folder.
   -o              Specifies the output file/folder path where to store the generated docs.
+  -open           Launches the browser when the server docs has started.
+  -p              Specifies the port to be used for the docs server.
   -s              Serve HTML-generated docs via HTTP.
   -r              Include README.md to docs if present.
   -v              Enables verbose logging. For debugging purposes.