lib/crypto: docs: Improve introduction sentence

Make it clear that lib/crypto/ is a kernel-internal library.  It's easy
for people to come across this page, especially the HTML version online,
without that context.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Link: https://patch.msgid.link/20260709022747.44635-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

Author: Eric Biggers

Documentation/crypto/libcrypto.rst

@@ -4,8 +4,9 @@
 Crypto library
 ==============
 
-``lib/crypto/`` provides faster and easier access to cryptographic algorithms
-than the traditional crypto API.
+The Linux kernel's crypto library (``lib/crypto/``) provides kernel-internal
+users of cryptographic algorithms with faster and easier access to those
+algorithms than the traditional kernel crypto API.
 
 Each cryptographic algorithm is supported via a set of dedicated functions.
 "Crypto agility", where needed, is left to calling code.