Add missing readme “Installation” section import map instructions for is-plain-obj.

Author: jaydenseric

changelog.md

@@ -4,6 +4,7 @@
 
 ### Patch
 
+- Added missing readme “Installation” section import map instructions for [`is-plain-obj`](https://npm.im/is-plain-obj).
 - Added [Browserslist](https://browsersl.ist) links to the readme.
 
 ## 19.0.0

readme.md

@@ -30,6 +30,8 @@ For [Deno](https://deno.land) and browsers, an example import map (realistically
   "imports": {
     "extract-files/": "https://unpkg.com/extract-files@12.0.0/",
     "graphql-react/": "https://unpkg.com/graphql-react@19.0.0/",
+    "is-plain-obj": "https://unpkg.com/is-plain-obj@4.1.0/index.js",
+    "is-plain-obj/": "https://unpkg.com/is-plain-obj@4.1.0/",
     "react": "https://esm.sh/react@18.2.0",
     "react-waterfall-render/": "https://unpkg.com/react-waterfall-render@4.0.1/"
   }
@@ -39,6 +41,7 @@ For [Deno](https://deno.land) and browsers, an example import map (realistically
 These dependencies might not need to be in the import map, depending on what [`graphql-react`](https://npm.im/graphql-react) modules the project imports from:
 
 - [`extract-files`](https://npm.im/extract-files)
+- [`is-plain-obj`](https://npm.im/is-plain-obj)
 - [`react-waterfall-render`](https://npm.im/react-waterfall-render)
 
 Polyfill any required globals (see [_**Requirements**_](#requirements)) that are missing in your server and client environments.