docs: more than 23 is not supported for CHUNK_MAX_EXP, fixes #3115

docs/misc/create_chunker-params.txt

@@ -7,6 +7,7 @@ CHUNK_MIN_EXP and CHUNK_MAX_EXP give the exponent N of the 2^N minimum and
 maximum chunk size. Required: CHUNK_MIN_EXP < CHUNK_MAX_EXP.
 
 Defaults: 19 (2^19 == 512KiB) minimum, 23 (2^23 == 8MiB) maximum.
+Currently it is not supported to give more than 23 as maximum.
 
 HASH_MASK_BITS is the number of least-significant bits of the rolling hash
 that need to be zero to trigger a chunk cut.