Add link to rustdoc instead of wiki (mimblewimble#264)

README.md

@@ -2,7 +2,7 @@
 [![Coverage Status](https://img.shields.io/codecov/c/github/mimblewimble/grin-wallet/master.svg)](https://codecov.io/gh/mimblewimble/grin-wallet)
 [![Chat](https://img.shields.io/gitter/room/grin_community/Lobby.svg)](https://gitter.im/grin_community/Lobby)
 [![Support](https://img.shields.io/badge/support-on%20gitter-brightgreen.svg)](https://gitter.im/grin_community/support)
-[![Documentation Wiki](https://img.shields.io/badge/doc-wiki-blue.svg)](https://github.com/mimblewimble/docs/wiki)
+[![](https://img.shields.io/badge/dynamic/json.svg?label=docs&uri=https%3A%2F%2Fcrates.io%2Fapi%2Fv1%2Fcrates%2Fgrin-wallet%2Fversions&query=%24.versions%5B0%5D.num&colorB=4F74A6)](https://docs.rs/releases/search?query=grin+wallet)
 [![Release Version](https://img.shields.io/github/release/mimblewimble/grin-wallet.svg)](https://github.com/mimblewimble/grin-wallet/releases)
 [![License](https://img.shields.io/github/license/mimblewimble/grin-wallet.svg)](https://github.com/mimblewimble/grin-wallet/blob/master/LICENSE)