document what the vector format is a little better (#4639)

diff --git a/vectors/cryptography_vectors/asymmetric/EC/compressed_points.txt b/vectors/cryptography_vectors/asymmetric/EC/compressed_points.txt
index 8df0a9b..d9bf5c0 100644
--- a/vectors/cryptography_vectors/asymmetric/EC/compressed_points.txt
+++ b/vectors/cryptography_vectors/asymmetric/EC/compressed_points.txt
@@ -1,4 +1,5 @@
 # Vectors generated by OpenSSL
+# POINT is hex encoded binary data while X and Y are hexadecimal integers
 
 COUNT = 0
 CURVE = SECP256R1