Improve documentation

Co-authored-by: Tom Cosgrove <81633263+tom-cosgrove-arm@users.noreply.github.com>
Co-authored-by: Werner Lewis <werner.wmlewis@gmail.com>
Co-authored-by: Minos Galanakis <minos.galanakis@arm.com>

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/library/bignum_mod_raw.h b/library/bignum_mod_raw.h
index 5e1418b..4b2a51f 100644
--- a/library/bignum_mod_raw.h
+++ b/library/bignum_mod_raw.h
@@ -1,5 +1,5 @@
 /**
- *  Low level modular bignum functions
+ *  Low-level modular bignum functions
  *
  *  This interface only should be used by the higher level modular bignum
  *  module (bignum_mod.c) and the ECP module (ecp.c, ecp_curves.c). All other