message: Add missing system props types to CONTRIBUTING
diff: @@ -111,6 +111,8 @@ Categories of system props are exported from `src/constants.js`:
  * `TYPOGRAPHY` includes font family, font weight, and line-height props
  * `POSITION` includes positioning props
  * `FLEX` includes flexbox props
  +* `BORDER` includes border and box-shadow props
  +* `GRID` includes grid props
  To give the component access to a group of system props, import the system prop function from `./constants` and include the system prop function in your styled-component like so:
  