Merge pull request #16345 from miri64/doc/enh/release-cycle

doc: README: Add documentation on downloads and release cycle

README.md

@@ -75,6 +75,30 @@ but not limited to:
 * Sigfox
 * LoRaWAN
 
+## GETTING RIOT
+
+The most convenient way to get RIOT is to clone it via Git
+
+```console
+$ git clone https://github.com/RIOT-OS/RIOT
+```
+
+this will ensure that you get all the newest features and bug fixes with the
+caveat of an ever changing work environment.
+
+If you prefer things more stable, you can download the source code of one of our
+quarter annual releases [via Github][releases] as ZIP file or tarball. You can
+also checkout a release in a cloned Git repository using
+
+```console
+$ git pull --tags
+$ git checkout <YYYY.MM>
+```
+
+For more details on our release cycle, check our [documentation][release cycle].
+
+[releases]: https://github.com/RIOT-OS/RIOT/releases
+[release cycle]: https://doc.riot-os.org/release-cycle.html
 
 ## GETTING STARTED
 * You want to start the RIOT? Just follow our

doc/doxygen/riot.doxyfile

@@ -774,6 +774,7 @@ INPUT                  = ../../doc.txt \
                          src/using-cpp.md \
                          src/advanced-build-system-tricks.md \
                          src/emulators.md \
+                         src/release-cycle.md \
                          src/changelog.md \
                          ../../LOSTANDFOUND.md
 

doc/doxygen/src/release-cycle.md

@@ -0,0 +1,57 @@
+Release cycle                                                   {#release-cycle}
+=============
+
+RIOT has a new release every three months and is named after the month it
+was feature frozen in. E.g. `2021.01` was feature frozen in January 2021.
+Feature freeze means the branch off point of the `<YYYY.MM>-branch` with
+`<YYYY.MM>` being the releases name. As such, any new feature merged into the
+`master` after that point, will be part of the next release. That branch, which
+we will call the release branch in the following is then the stable branch of
+RIOT.
+
+After feature freeze, the current release candidate in the release branch is
+tested heavily. For more information on the release testing, have a look at our
+[release specifications][release specs]. Bug fixes that are made during this
+testing period are back ported from `master` to the release branch and a new
+release candidate might be created when a certain milestone is found. If all
+major bugs are fixed, the new RIOT release is signed off by the appointed
+release manager, usually within 2 weeks after the feature freeze.
+
+RIOT follows a rolling release cycle, meaning, that support and bug fixes are
+only provided for the most current release.
+
+Download a release                                                   {#download}
+==================
+
+You can download the source code of our releases [via Github][releases] as ZIP
+file or tarball. Alternatively, you can check them out if you already cloned
+RIOT with Git:
+
+~~~~~~~~~~~~~~~~~~~~
+$ git pull --tags
+$ git checkout <YYYY.MM>
+~~~~~~~~~~~~~~~~~~~~
+
+Point releases and hot fixes                                   {#point-releases}
+============================
+
+For major bug fixes, we may provide a point release `YYYY.MM.N` which results in
+a new ZIP file or tarball over at the [release page][releases]. However, minor
+bug fixes are only pushed to the release branch. You can fetch that via Git
+using
+
+~~~~~~~~~~~~~~~~~~~~
+$ git clone -b `<YYYY.MM>-branch` https://github.com/RIOT-OS/RIOT
+~~~~~~~~~~~~~~~~~~~~
+
+or
+
+~~~~~~~~~~~~~~~~~~~~
+$ git pull origin <YYYY.MM-branch>:<YYYY.MM-branch>
+$ git checkout <YYYY.MM-branch>
+~~~~~~~~~~~~~~~~~~~~
+
+if you have RIOT already cloned.
+
+[releases]: https://github.com/RIOT-OS/RIOT/releases
+[release specs]: https://github.com/RIOT-OS/Release-Specs