Add React to main nav and Homepage

[darylldoyle]

Description of the Change

This PR moves React from being a sub-page of JavaScript to being its own main page. This makes it easier to link to certain parts of the React practices as they can be anchored to.

Verification Process

Tested locally.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

#307

Changelog Entry

• Changed React from being a JavaScript sub-page to a page of its own.