Add a short description of what each module does
There was already a short introduction to _who_ should use each module, but
not to _what_ each module does.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/bignum_core.h b/library/bignum_core.h
index dc802ab..d64111b 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -6,6 +6,11 @@
* modules should use the high-level modular bignum interface (bignum_mod.h)
* or the legacy bignum interface (bignum.h).
*
+ * This module is about processing non-negative integers with a fixed upper
+ * bound that's of the form 2^#biL-1. Many operations treat these numbers
+ * as the principal representation of a number modulo 2^#biL or a smaller
+ * bound.
+ *
*/
/*