Add plugin and watcher docs

content/roadmaps/105-vue/content/101-advanced-topics/112-plugins.md

@@ -1 +1,6 @@
 # Plugins
+
+Plugins are self-contained code that usually add app-level functionality to Vue. 
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='blue' badgeText='Official Docs' href='https://vuejs.org/guide/reusability/plugins.html'>Plugins in Vue.js</BadgeLink>

content/roadmaps/105-vue/content/101-advanced-topics/113-watchers.md

@@ -1 +1,8 @@
 # Watchers
+
+Computed properties allow us to declaratively compute derived values. However, there are cases where we need to perform "side effects" in reaction to state changes - for example, mutating the DOM, or changing another piece of state based on the result of an async operation.
+
+With Composition API, we can use the watch function to trigger a callback whenever a piece of reactive state changes.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='blue' badgeText='Official Docs' href='https://vuejs.org/guide/essentials/watchers.html'>Watchers in Vue.js</BadgeLink>