[README] dysfun explanation of how using this RFC repo, copy/pasted from IRC.

README.md

+# HOW TO USE THIS RFC REPO
+
+All major structural changes to Gargantext code base (Backend and
+Frontend) go through an RFC, a request for comment, much like IETF
+standards for the internet
+
+These are actually stored as documents in a repo (in markdown iirc).
+Adding a feature to Gargantext typically starts with filing an issue to
+discuss it.
+
+If it's not decided it's a bad idea, the originator will typically
+create a PR to add a formal specification for the feature to the repo
+through discussion, eventually a satisfactory text is arrived at PR is
+merged feature can then be written.
+
+## Credits
+- thanks to dysfun for this idea of RFC repo (stolen from Rust-RFC ;)
+