Update ToC in README file

Author: ahangarha

README.md

@@ -68,13 +68,16 @@ Read the [full review here](https://clutch.co/profile/shakacode#reviews?sort_by=
 - [Upgrading](#upgrading)
   - [2.7 to 3.0](#27-to-30)
   - [2.3 to 2.4](#23-to-24)
+- [Other features](#other-features)
+  - [Replace `null` with `undefined` in props](#replace-null-with-undefined-in-props)
 - [Common Errors](#common-errors)
   - [Getting warning for `Can't resolve 'react-dom/client'` in React < 18](#getting-warning-for-cant-resolve-react-domclient-in-react--18)
   - [Undefined Set](#undefined-set)
   - [Using TheRubyRacer](#using-therubyracer)
   - [HMR](#hmr)
 - [Related Projects](#related-projects)
 - [Contributing](#contributing)
+- [Supporters](#supporters)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
@@ -876,7 +879,7 @@ By contributing to React-Rails, you agree to abide by the [code of conduct](http
 
 You can always help by submitting patches or triaging issues. Even offering reproduction steps to issues is incredibly helpful!
 
-# Supporters
+## Supporters
 
 The following companies support the development of this and other open-source projects maintained by ShakaCode by providing licenses to the ShakaCode team. ShakaCode stands by the usefulness of these products!