Add settings menu (^S)

README.md

@@ -59,7 +59,8 @@ unconfigured nginx container.
 
 ### Editing a document
 
-1. Run `jsonedit <filename>` from your shell.
+1. Run `jsonedit <filename>` from your shell, or run `jsonedit` and press **^O**
+   to browse for a file to open.
 2. Find the value you want to edit and press **e**.
 3. Enter the value usng valid JSON value encoding, for example `"1234"` for the
    string 1234, and `1234` for the integer 1234. Unparsable JSON will be used
@@ -88,6 +89,7 @@ exists.
 - **t** - Toggle tail line guide
 - **b** - Toggle icons before keys
 - **c** - Toggle compact mode
+- **^S** - Open settings menu
 
 ## Caveats