reorder the primitives list and improve a few titles (#3640)

diff --git a/docs/hazmat/primitives/cryptographic-hashes.rst b/docs/hazmat/primitives/cryptographic-hashes.rst
index 55af21a..521ae09 100644
--- a/docs/hazmat/primitives/cryptographic-hashes.rst
+++ b/docs/hazmat/primitives/cryptographic-hashes.rst
@@ -1,7 +1,7 @@
 .. hazmat::
 
-Message digests
-===============
+Message digests (Hashing)
+=========================
 
 .. module:: cryptography.hazmat.primitives.hashes