Add a note that pulp-glue follows semver

Author: mdellweg

pulp-glue/README.md

@@ -1,2 +1,2 @@
 # Pulp Glue
-## The version agnostic Pulp 3 client library in python
+## The version agnostic Pulp 3 client library in Python

pulp-glue/docs/dev/index.md

@@ -0,0 +1,17 @@
+# Welcome to Pulp Glue
+
+## The version agnostic Pulp 3 client library in Python
+
+Pulp Glue is developed for and with the [Pulp CLI] in a combined repository.
+Therefore they share a common [changelog] and release corresponding versions.
+
+## Versioning Policy
+
+Pulp Glue follows semantic versioning (SemVer) compatibility.
+That is, with the one known exception that a new y-version does not necessarily imply a new feature to be available.
+This is a result from releasing in lock-step with `pulp-cli`.
+To stay compatible we advise to define the dependency as `pulp-glue=>x1.y1.z1,<x2.y2`.
+If you just want to avoid breaking changes, you can also settle on `pulp-glue=>x1.y1.z1,<x2`.
+
+[Pulp CLI]: site:pulp-cli/
+[changelog]: site:pulp-cli/changes/