docs(guide/modules): Add examples for mapGetters with namespace (#1782)

Author: michapietsch

Diff for: docs/guide/modules.md

@@ -209,7 +209,11 @@ computed: {
   ...mapState({
     a: state => state.some.nested.module.a,
     b: state => state.some.nested.module.b
-  })
+  }),
+  ...mapGetters([
+    'some/nested/module/someGetter', // -> this['some/nested/module/someGetter']
+    'some/nested/module/someOtherGetter', // -> this['some/nested/module/someOtherGetter']
+  ])
 },
 methods: {
   ...mapActions([
@@ -226,7 +230,11 @@ computed: {
   ...mapState('some/nested/module', {
     a: state => state.a,
     b: state => state.b
-  })
+  }),
+  ...mapGetters('some/nested/module', [
+    'someGetter', // -> this.someGetter
+    'someOtherGetter', // -> this.someOtherGetter
+  ])
 },
 methods: {
   ...mapActions('some/nested/module', [