Merge bitcoin#1002: BIP155: Mention SHA3-256 explicitly

6ef71b3 BIP155: Small text improvements (Hennadii Stepanov)
562f1d7 BIP155: Mention SHA3-256 explicitly (Hennadii Stepanov)

Pull request description:

  It seems better to clarify that `CHECKSUM` in Tor onion v3 address uses SHA3-256 hash function.

ACKs for top commit:
  vasild:
    ACK 6ef71b3
  laanwj:
    ACK 6ef71b3

Tree-SHA512: b88c7dfeeda2a99cfe1042c9f4e7cbeb6047882bf97ce9c1dd5e1f4a30203a9a03702638cc4b6c3b573f6c0a05b73a5ca43a77352a5ca24a32d19be129f8b317

Author: laanwj

bip-0155.mediawiki

@@ -150,7 +150,7 @@ The reference implementation is available at (to be done)
 
 ==Appendix A: Tor v2 address encoding==
 
-The new message introduces a separate network ID for <code>TORV2</code>. 
+The new message introduces a separate network ID for <code>TORV2</code>.
 
 Clients MUST send Tor hidden service addresses with this network ID, with the 80-bit hidden service ID in the address field. This is the same as the representation in the legacy <code>addr</code> message, minus the 6 byte prefix of the OnionCat wrapping.
 
@@ -164,10 +164,11 @@ onion_address = base32(PUBKEY | CHECKSUM | VERSION) + ".onion"
  CHECKSUM = H(".onion checksum" | PUBKEY | VERSION)[:2]
 
  where:
-   - PUBKEY is the 32 bytes ed25519 master pubkey of the hidden service.
-   - VERSION is an one byte version field (default value '\x03')
+   - PUBKEY is the 32 bytes ed25519 master pubkey of the hidden service
+   - VERSION is a one byte version field (default value '\x03')
    - ".onion checksum" is a constant string
    - CHECKSUM is truncated to two bytes before inserting it in onion_address
+   - H() is the SHA3-256 cryptographic hash function
 </pre>
 
 Tor v3 addresses MUST be sent with the <code>TORV3</code> network ID, with the 32-byte PUBKEY part in the address field. As VERSION will always be '\x03' in the case of v3 addresses, this is enough to reconstruct the onion address.