fixed the spelling error

[bandu7]

added is in the sentence

You're looking into contributing? Awesome! When contributing to this mono-repository, please first discuss the change you wish to make via the discussion board with me before making a change. Before submitting a pull request, please make sure the following is done:

• Create a public fork the React Unity WebGL mono-repository and commit your changes to a new branch which is based from the original repository's main branch.
• Make sure both the module as well as the documentation installs using npm install, your code lints using ts lint, is formatted using prettier and compiles using npm run build.
• Typecheck all of your changes and make sure the documentation in both the source code as well as the official website is up to date and reflects the changes you've made.
• Make sure your changes passes and are compatibly with Unity WebGL builds using the testing suite.

[jeffreylanters]

Thanks for your contribution!