docs: Added clarifications to the behaviour of plugin:install and plu…

…gin:link (#45)

README.md

@@ -104,6 +104,11 @@ EXAMPLE
 
 _See code: [src/commands/plugins/install.ts](https://github.com/oclif/plugin-plugins/blob/v1.2.0/src/commands/plugins/install.ts)_
 
+**NOTE**:
+
+    Installation of a user-installed plugin will override a core plugin. 
+e.g. If you have a core plugin that has a 'hello' command, installing a user-installed plugin with a 'hello' command will override the core plugin implementation. This is useful if a user needs to update core plugin functionality in the CLI without the need to patch and update the whole CLI.
+
 ## `mycli plugins:link PLUGIN`
 
 links a plugin into the CLI for development
@@ -125,6 +130,11 @@ EXAMPLE
 
 _See code: [src/commands/plugins/link.ts](https://github.com/oclif/plugin-plugins/blob/v1.2.0/src/commands/plugins/link.ts)_
 
+**NOTE**:
+
+    Installation of a linked plugin will override a user-installed or core plugin.
+e.g. If you have a user-installed or core plugin that has a 'hello' command, installing a linked plugin with a 'hello' command will override the user-installed or core plugin implementation. This is useful for development work.
+
 ## `mycli plugins:uninstall PLUGIN...`
 
 removes a plugin from the CLI