docs: add alias example in package-json docs

docs/lib/content/configuring-npm/package-json.md

@@ -617,6 +617,7 @@ See [semver](https://github.com/npm/node-semver#versions) for more details about
 * `tag` A specific version tagged and published as `tag`  See [`npm
   dist-tag`](/commands/npm-dist-tag)
 * `path/path/path` See [Local Paths](#local-paths) below
+* `npm:@scope/pkg@version` Custom alias for a pacakge See [`npm install`](/commands/npm-install) 
 
 For example, these are all valid:
 
@@ -634,7 +635,8 @@ For example, these are all valid:
     "two": "2.x",
     "thr": "3.3.x",
     "lat": "latest",
-    "dyl": "file:../dyl"
+    "dyl": "file:../dyl",
+    "kpg": "npm:pkg@1.0.0"
   }
 }
 ```