ipip-512: clarify limit applies to digest size

addressing feedback from
#512 (review)

Author: lidel

src/ipips/ipip-0512.md

@@ -53,8 +53,8 @@ This IPIP adds a new section to the UnixFS specification documenting the 128-byt
 Add new section "Identity CID Size Limit" that specifies:
 
 - Identity CIDs (multihash code `0x00`) are experimental and limited to 128-byte digest size
-- Implementations MUST never produce identity CIDs exceeding 128 bytes
-- Implementations MUST reject identity CIDs exceeding 128 bytes when reading
+- Implementations MUST never produce identity CIDs with digest sizes exceeding 128 bytes
+- Implementations MUST reject identity CIDs with digest sizes exceeding 128 bytes when reading
 - Implementations SHOULD automatically convert to regular blocks if data modifications would exceed the limit
 
 ### Test Fixtures