[doc][readme] Add instructions to start the application

doc/README.md

@@ -14,9 +14,20 @@ toolchain editor in `beat.web`.
 
 To install, just run `conda install beat.editor`.
 
+
 ### Use
 
-**TBD**
+To start the main beat.editor application:
+
+    $ beat editor start
+
+This will show the main application Window which will allow to browse the prefix
+configured or selected by the user.
+
+For more information about the options that can be used with the application:
+
+    $ beat editor --help
+
 
 ### Development
 > See `contribute`