Merge pull request #582 from kenjis/fix-docs-install.md

docs: improve installation instruction

Author: datamweb

docs/install.md

@@ -40,11 +40,11 @@ Could not find a version of package codeigniter4/shield matching your minimum-st
 Require it with an explicit version constraint allowing its desired stability.
 ```
 
-1. Add the following to change your [minimum-stability](https://getcomposer.org/doc/articles/versions.md#minimum-stability) in your project `composer.json`:
+1. Run the following commands to change your [minimum-stability](https://getcomposer.org/doc/articles/versions.md#minimum-stability) in your project `composer.json`:
 
-    ```json
-    "minimum-stability": "dev",
-    "prefer-stable": true,
+    ```console
+    composer config minimum-stability dev
+    composer config prefer-stable true
     ```
 
 2. Or specify an explicit version: