Add newsletter entry for libMesh namespace inclusion removal

modules/doc/content/newsletter/2024/2024_10.md

@@ -7,6 +7,20 @@ for a complete description of all MOOSE changes.
 
 ## MOOSE Improvements
 
+### Removing default inclusion of the entire libMesh namespace
+
+The entirety of the `libMesh` namespace is no longer introduced by the `Moose.h` header. This was removed
+in order to prevent conflict between namespaces of external libraries that could be used by MOOSE-based
+applications.
+A reduced number of `libMesh` namespace objects are still included through the `libMeshReducedNamespace.h`.
+This list will be adjusted, mostly further reduced, over time.
+
+In order to continue to use `libMesh` namespace objects, we recommend:
+
+- prefacing objects with the namespace name, for example `libMesh::ValueValue` for a `VectorValue`
+- in source files, you may add `using namespace libMesh;` in order not to require such prefixes
+- in header files, doing so is not generally recommended, the use of prefixes should be preferred
+
 ## libMesh-level Changes
 
 ## PETSc-level Changes