update compatibility table with comments and v4.3.0

Author: tomeichlersmith

src/developing/compatibility.md

@@ -102,7 +102,7 @@ no det id bindings | >= v3.2, < v5.0.0
 no det id bindings and no sanitizers | >= v3.0, < v5.0.0
 header patch | >= v5.0.0
 
-### >= v3.3.5, < v4.2.15
+### >= v3.3.5, < v4.3.0
 Updates to the ROOT dictionary generation procedure inadvertently
 broke compatibility with older container images.
 Users of older container images will see issues during dictionary building
@@ -118,7 +118,13 @@ build config | image version
 default | >= v4.0.0, < v5.0.0
 header patch | >= v5.0.0
 
-### >= v4.2.15
+Compiler patches necessary to work well with ldmx/dev:5.0.0 were initially
+introduced in ldmx-sw:v4.2.15; however, ongoing development required other
+patches to be included as well.
+It is encouraged to rebase and/or merge ldmx-sw:v4.3.0 into your branch in
+order for the main CI tests to work now that they use ldmx/dev:5.0.0.
+
+### >= v4.3.0
 Patches for the newer compiler have been included and so the default build
 configuration can be handled by the new image version.
 Not all of the _warnings_ from the newer compiler have been patched,