doc/release: Describe development version designation

After each release version will be changed to
MAJOR.MINOR.PATCH-dev.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/docs/release.md b/docs/release.md
index 34bd5c3..3115b6d 100644
--- a/docs/release.md
+++ b/docs/release.md
@@ -15,6 +15,9 @@
 
 We add pre-release tags of the format MAJOR.MINOR.PATCH-rc1.
 
+We mark in documentation an MCUBoot development version using
+the format MAJOR.MINOR.PATCH-dev.
+
 ## Release Notes
 
 Before making a release, be sure to update the `docs/release-notes.md`
@@ -81,4 +84,17 @@
 git push origin va.b.c-rcn
 ```
 
+## Post release actions
+
+Mark the MCUBoot version as a development version. The version number used
+should be specified for the next expected release.
+It should be larger than the last release version by incrementing the MAJOR or
+the MINOR number. It is not necessary to define the next version precisely as
+the next release version might still be different as it might be needed to do:
+
+- a patch release
+- a MINOR release while a MAJOR release was expected
+- a MAJOR release while a MINOR release was expected
+
+
 [semver]: http://semver.org/