[FIX Readme] Nodejs + Python version spicifications (#11181)

* Nodejs + Python version spicifications

I spent more than 10 hours on the building Rocket.Chat with Python v3.x and NodeJS v9.x!
Rocket.Chat is compatible (only?) with NodeJS v8.9.3 and Python v2.7
Merge this and save lives! Thank you

* Update README.md

README.md

@@ -392,6 +392,8 @@ Prerequisites:
 * [Git](http://git-scm.com/book/en/v2/Getting-Started-Installing-Git)
 * [Meteor](https://www.meteor.com/install)
 
+> Meteor automatically installs a hidden [NodeJS v8](https://nodejs.org/download/release/v8.9.3/), [Python v2.7](https://www.python.org/downloads/release/python-270/) and [MongoDB v3.6](https://www.mongodb.com/mongodb-3.6) to be used when you run your app in development mode using the `meteor` command.
+
 Now just clone and start the app:
 
 ```sh