[docs] move docs on disabling packagist to repositories chapter, fixes #362

doc/04-schema.md

@@ -288,17 +288,6 @@ Example:
 precedence. This also means that custom repositories can override packages
 that exist on packagist.
 
-You can also disable the packagist repository by setting `packagist` to
-`false`.
-
-    {
-        "repositories": [
-            {
-                "packagist": false
-            }
-        ]
-    }
-
 ## config
 
 A set of configuration options. It is only used for projects.

doc/05-repositories.md

@@ -249,3 +249,16 @@ package repository definitions. It will fetch all the packages that are
 
 Check [the satis GitHub repository](https://github.com/composer/satis) for more
 information.
+
+## Disabling packagist
+
+You can disable the default packagist repository by adding this to your
+`composer.json`:
+
+    {
+        "repositories": [
+            {
+                "packagist": false
+            }
+        ]
+    }