bip-0325: correct byte count for compact size, and tweak to header name

bip-0325.mediawiki

@@ -28,8 +28,8 @@ A new type of network ("signet"), which takes an additional consensus parameter
 
 The witness commitment of the coinbase transaction is extended to include a secondary commitment (the signature/solution) of either:
 
-    1-4 bytes - Push the following (4 + x + y) bytes
-    4 bytes - Signet scriptSig header (0xecc7daa2)
+    1-5 bytes - Push the following (4 + x + y) bytes
+    4 bytes - Signet header (0xecc7daa2)
     x bytes - scriptSig
     y bytes - scriptWitness