slip-0173: add (#1386)

slip-0173.md

@@ -135,6 +135,7 @@ These are the registered human-readable parts for usage in Bech32 encoding of wi
 | [Shimmer](https://shimmer.network)              | `smr`         | `rms`   |             |
 | [Sifchain](https://sifchain.finance/)           | `sif`         |         |             |
 | [Sommelier](https://sommelier.finance)          | `somm`        |         |             |
+| [Spacemesh](https://spacemesh.io/)              | `sm`          | `stest` |             |
 | [Stargaze](https://stargaze.zone/)              | `stars`       |         |             |
 | [Starname](https://www.starname.me/)            | `star`        |         |             |
 | [Straightedge](http://straighted.ge/)           | `str`         |         |             |