Add libMesh update details to newsletter

modules/doc/content/newsletter/2021_10.md

@@ -101,4 +101,23 @@ Some examples of MOOSE mortar constraints (previously available only in 2D) incl
 
 ## libMesh-level Changes
 
+- Support for Tri7 triangles (like Tri6 plus with one mid-element
+  node) and Tet14 tetrahedra (like Tri10 plus one mid-face node on
+  each face)
+- Reduced Basis EIM updates
+- SIDE\_HIERARCHIC finite element (shapes defined on sides and
+  discontinuous between sides) support for triangles
+- LOG\_CALL() macro to simplify exception-safe PerfLog support in more
+  use cases.
+- Refactoring and simplification of the finite-difference-method
+  fallback for calculating shape function gradients on finite element
+  types without analytic gradient implementations
+- ExodusII\_IO::get\_sideset\_data\_indices() accessor method
+- Fixed file handle leaks in some ExodusII use cases, leaks which
+  triggered errors when running with ExodusII version 8.11
+- Read support for new IsoGeometric Analysis extensions to ExodusII
+- Assorted bug fixes for distcheck, clang warnings,
+  non-double-precision configurations, Elem::permute(), other minor
+  issues. 
+
 ## Bug Fixes and Minor Enhancements