message: update readme for handleKeys config option
diff: @@ -49,7 +49,11 @@ Below is an example of a [settings.json](https://code.visualstudio.com/Docs/cust
  "after": ["d", "d"]
  }
  ],
  - "vim.leader": "<space>"
  + "vim.leader": "<space>",
  + "vim.handleKeys":{
  + "<C-a>": false,
  + "<C-f>": false
  + }
  }
  ```
  @@ -72,6 +76,17 @@ The following is a subset of the supported configurations; the full list is desc
  "vim.useCtrlKeys": true
  ```
  +#### handleKeys
  + * Allows user to select certain modifier keybindings and delegate them back to VSCode so that VSCodeVim does not process them.
  + * An example would be if a user wanted to continue to use ctrl + f for find, but wants to have useCtrlKeys set to true so that other vim bindings work.
  +
  + ```
  + "vim.handleKeys":{
  + "<C-a>": false,
  + "<C-f>": false
  + }
  + ```
  +
  #### insertModeKeyBindings/otherModesKeyBindings
  * Keybinding overrides to use for insert and other (non-insert) modes.
  