Clarify testnets

Author: Robert Spigler

Modern Derivation Standard.mediawiki

@@ -86,7 +86,7 @@ Sharing the same space for various networks has some disadvantages.
 
 This level creates a separate subtree for every network, avoiding reusing addresses across networks and improving privacy issues.
 
-Coin type <code>0</code> for mainnet and <code>1</code> for testnet.
+Coin type <code>0</code> for mainnet and <code>1</code> for testnets (testnet, regtest, and signet).
 
 Hardened derivation is used at this level.