Build guide link broken

https://iroha.readthedocs.io/en/latest/build/index.html is a working
link to build iroha
Signed-off-by: Eric Curtin <ericcurtin17@gmail.com>

README.md

@@ -45,7 +45,7 @@ Check [getting started](http://iroha.readthedocs.io/en/latest/getting_started/)
 
 ### How to build Iroha?
 
-Use [build guide](http://iroha.readthedocs.io/en/latest/guides/build.html), which might be helpful if you want to modify the code and contribute.
+Use [build guide](https://iroha.readthedocs.io/en/latest/build/index.html), which might be helpful if you want to modify the code and contribute.
 
 ### Is there SDK available?