add global find keyword

src/background/actions/find.js

@@ -0,0 +1,10 @@
+import actions from './index';
+
+const setKeyword = (keyword) => {
+  return {
+    type: actions.FIND_SET_KEYWORD,
+    keyword,
+  };
+};
+
+export { setKeyword };

src/background/actions/index.js

@@ -2,4 +2,7 @@ export default {
   // Settings
   SETTING_SET_SETTINGS: 'setting.set.settings',
   SETTING_SET_PROPERTY: 'setting.set.property',
+
+  // Find
+  FIND_SET_KEYWORD: 'find.set.keyword',
 };