Document user-visible changes

doc/user-changes.md

@@ -4,7 +4,20 @@ This document is a development diary summarizing changes in `alr` that notably
 affect the user experience. It is intended as a one-stop point for users to
 stay on top of `alr` new features.
 
-## Use a directory to fulfill a dependency (2020-05-17)
+## Allow working with incomplete solutions (2020-06-17)
+
+PR [#447](https://github.com/alire-project/alire/pull/447).
+
+Before this patch, any change in dependences that resulted in an incomplete
+solution caused a final "invalid solution" error. Now, any incomplete solution
+will be presented to the user with details about the unfulfilled dependencies.
+This solution can be accepted and worked with normally, although the user is
+responsible to provide in the environment any missing project files.
+
+This change affects all commands that compute a dependency solution, i.e.,
+`get`, `pin`, `update`, `with`.
+
+## Use a directory to fulfill a dependency (2020-06-17)
 
 A local path can now be used to fulfill a dependency. The path can be supplied
 during initial dependency addition or afterwards during pinning, via the