Add a custom logo to our docs

As suggested in #497, add our logo to the docs as well

src/lib.rs

@@ -14,6 +14,10 @@
 // only enables the `doc_cfg` feature when
 // the `docsrs` configuration attribute is defined
 #![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(
+    docsrs,
+    doc(html_logo_url = "https://github.com/bitcoindevkit/bdk/raw/master/static/bdk.png")
+)]
 
 //! A modern, lightweight, descriptor-based wallet library written in Rust.
 //!