Add release notes for the 3.0 release (#142)

spec/src/main/asciidoc/release_notes.asciidoc

@@ -17,6 +17,17 @@
 // limitations under the License.
 //
 
+[[release_notes_30]]
+== Release Notes for MicroProfile Reactive Messaging 3.0
+
+A full list of changes delivered in the 3.0 release can be found at link:https://github.com/eclipse/microprofile-reactive-messaging/milestone/8[MicroProfile Reactive Messaging 3.0 Milestone].
+
+==== Incompatible Changes
+This release aligns with Jakarta EE 9.1 (link:https://github.com/eclipse/microprofile-reactive-messaging/issues/137[137]), so it won't work with earlier versions of Jakarta or Java EE.
+
+==== API/SPI Changes
+There are no functional changes introduced in this release, except the dependency updating from javax to jakarta.
+
 [[release_notes_20]]
 == Release Notes for MicroProfile Reactive Messaging 2.0