Add RevX to the list of development tools

[leonardocustodio]

Added RevX as an online IDE for Polkadot contract development.

Checklist

• The URL is not already present in the list (check with CTRL/CMD+F in the raw markdown file).
• Each description starts with an uppercase character and ends with a period.
  Example: solc-js - JavaScript bindings for the compiler.
• Drop all A / An prefixes at the start of the description.

[vercel]

@leonardocustodio is attempting to deploy a commit to the Personal Team on Vercel.

A member of the Team first needs to authorize it.