Add link to alpha4 release notes

docs/reference/release-notes.asciidoc

@@ -5,12 +5,14 @@
 --
 This section summarizes the changes in each release.
 
+* <<release-notes-5.0.0-alpha4>>
 * <<release-notes-5.0.0-alpha3>>
 * <<release-notes-5.0.0-alpha2>>
 * <<release-notes-5.0.0-alpha1>>
 * <<release-notes-5.0.0-alpha1-2x>>
 
 --
+include::release-notes/5.0.0-alpha4.asciidoc[]
 include::release-notes/5.0.0-alpha3.asciidoc[]
 include::release-notes/5.0.0-alpha2.asciidoc[]
 include::release-notes/5.0.0-alpha1.asciidoc[]