Add SLIP-0173 (#77)

slip-0173.md

+# SLIP-0173 : Registered human-readable parts for BIP-0173
+
+```
+Number:  SLIP-0173
+Title:   Registered human-readable parts for BIP-0173
+Type:    Standard
+Status:  Draft
+Authors: Clark Moody <clark@clarkmoody.com>
+Created: 2017-05-17
+```
+
+## Abstract
+
+BIP-0173 defines a new format for segregated witness output addresses that contains a human-readable part that identifies the coin type.
+
+## Motivation
+
+The BIP repository does not want to deal with assigning the values for various coin types different than Bitcoin so we propose this SLIP to become such body.
+
+## Registered human-readable parts
+
+These are the registered human-readable parts for usage in Bech32 encoding of witness programs.
+
+hrp  | coin
+-----|--------------------------------
+`bc` | [Bitcoin](https://bitcoin.org/)
+`tb` | Bitcoin Testnet
+
+## Libraries
+
+* [Reference Implementations](https://github.com/sipa/bech32/tree/master/ref)
+
+## References
+
+* [BIP-0173: Base32 address format for native v0-16 witness outputs](https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki)