[build-deps] Explain major versions and branches in README (#2544)

README.md

@@ -166,6 +166,18 @@ This will require some PHP-related tools to run, for instance on Ubuntu you will
 On every commit on the master branch (including merged Pull Requests) a new release will be created and 
 available at [daily releases](https://reva-releases.web.cern.ch/reva-releases).
 
+## Major versions
+
+There are currently two major versions in active development.
+
+### 1.x versions
+
+The ``master`` branch is the stable development branch. Releases from master are tagged as 1.x.x versions following [semver](https://semver.org/).
+
+### 2.x versions
+
+The ``edge`` branch is used to develop the next version of this project. The edge branch is based on a new concept named "Spaces" and a new set of the CS3APIs are being implemented, making it **not compatible** with `master` branch. Releases from `edge` are tagged as *2.x.x* versions following [semver](https://semver.org/).
+
 ## Run it using Docker
 
 See [https://hub.docker.com/r/cs3org/reva](https://hub.docker.com/r/cs3org/reva).