clarify wire format is binary encoded prototbuf (#1538)

Signed-off-by: Josh Marinacci <276938+joshmarinacci@users.noreply.github.com>

Author: joshmarinacci

HIP/hip-1261.md

@@ -466,7 +466,7 @@ The validation process checks the following, in any order:
 
 ### Schema
 
-The schema is defined in Protobuf. The wire format is JSON.
+The schema is defined in Protobuf. The wire format is binary encoded Protobuf.
 
 ```protobuf
 import "services/basic_types.proto";