Update README

Author: MFransen69

README

@@ -14,8 +14,14 @@ To build and use the buildroot stuff, do the following:
 5) find the kernel, bootloader, root filesystem, etc. in output/images
 
 This repo consist of mutliple branches:
+- Rx (e.g. R4). This is a release branch (the latest release is the default branch)
+These are branches on which a certain version of Thunder and it's related components (e.g. plugins and client libraries) are released.
+These are tested by QA and when approved for release, a release on that branch is created  (so with a tag to be able to checkout this specific version) 
+which includes the QA report. 
+Use these branches when a stable version needs to be build (e.g. take the latest released version tag on the R4 branch)
 - main: this branch contains the latest contributions but the hashes for packages will not be updated regularly. 
-Use this branch when you want to work on some of the packages and typically you would use a local override to bump related packes to the latest version (e.g. Thunder and its components)
+Use this branch when you want to work on some of the packages and typically you would use a local override to bump related packes 
+to the latest version (e.g. Thunder and its components)
 
 You do not need to be root to build or run buildroot.  Have fun!