Fix documentation

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/bignum_core.h b/library/bignum_core.h
index 3a11160..5750656 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -401,6 +401,8 @@
 /**
  * \brief Perform a known-size multiplication
  *
+ * \p A may be aliased to \p B.
+ *
  * \param[out] X     The pointer to the (little-endian) array to receive
  *                   the product of \p A_limbs and \p B_limbs.
  *                   This must be of length \p A_limbs + \p B_limbs.