fix: docs failing to build (#334)

Added #![cfg_attr(docsrs, feature(doc_cfg))]

fixes #333
Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

src/lib.rs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+#![cfg_attr(docsrs, feature(doc_cfg))]
 #![allow(unknown_lints)]
 #![allow(clippy::doc_lazy_continuation)]
 // Use README.md as crate documentation.