Put some graphics in the README? (#5930)

* Update README.md

I didn't do a good job at making the gif, but this is just a proposal.

If accepted, I can make a better one or ask Max to help with it.

* better gif file

* New file

substrate/README.md

 # Substrate · [![GitHub license](https://img.shields.io/github/license/paritytech/substrate)](LICENSE) [![GitLab Status](https://gitlab.parity.io/parity/substrate/badges/master/pipeline.svg)](https://gitlab.parity.io/parity/substrate/pipelines) [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg)](docs/CONTRIBUTING.adoc)
 
-Substrate is a next-generation framework for blockchain innovation.
+<p align="center">
+  <img src="/docs/media/sub.gif">
+</p>
+
+
+Substrate is a next-generation framework for blockchain innovation 🚀.
 
 ## Trying it out