Clarify activation of search plugin

Author: timvink

README.md

@@ -21,13 +21,16 @@ Install the plugin using pip:
 pip install mkdocs-git-authors-plugin
 ```
 
-Activate the plugin in `mkdocs.yml`:
+Next, add the following lines to your `mkdocs.yml`:
 
-```yaml
+```yml
 plugins:
+  - search
   - git-authors
 ```
 
+> If you have no `plugins` entry in your config file yet, you'll likely also want to add the `search` plugin. MkDocs enables it by default if there is no `plugins` entry set.
+
 ## Usage
 
 ### In supported themes