fix compilation of the doc and started a page dedicated to high performance and or BLAS users
diff --git a/doc/snippets/MatrixBase_asDiagonal.cpp b/doc/snippets/MatrixBase_asDiagonal.cpp
index 4cbff82..b01082d 100644
--- a/doc/snippets/MatrixBase_asDiagonal.cpp
+++ b/doc/snippets/MatrixBase_asDiagonal.cpp
@@ -1 +1 @@
-cout << Vector3i(2,5,6).asDiagonal() << endl;
+cout << Matrix3i(Vector3i(2,5,6).asDiagonal()) << endl;