[doc] Fix markdown

doc/README.md

@@ -49,7 +49,7 @@ The following are developer notes on how to build Bitcoin on your native platfor
 
 Development
 ---------------------
-The Bitcoin repo's [root README](https://github.com/bitcoin/bitcoin/blob/master/README.md) contains relevant information on the development process and automated testing.
+The Bitcoin repo's [root README](/README.md) contains relevant information on the development process and automated testing.
 
 - [Developer Notes](developer-notes.md)
 - [Multiwallet Qt Development](multiwallet-qt.md)