README: add release instructions

README.md

@@ -119,6 +119,15 @@ UDP multicast address 239.255.0.100:30000. To receive them you can use [socat][]
 
     $ socat udp4-recv:30000,ip-add-membership=239.255.0.100:0.0.0.0 -
 
+# Publishing a release (for maintainers)
+
+Pushing a tag in the form `v0.56` will create a new release and build
+`pkgj.vpk`.
+
+If you want to build a beta, you can push a tag in the form `v0.56-beta1` which
+will create a pre-release. Such a release will not be picked up by the auto
+update.
+
 # License
 
 This software is released under the 2-clause BSD license.