link to omegaconf custom resolvers to fix 2839 (#2881)

Author: gerard-sanroma

website/docs/configure_hydra/Intro.md

@@ -154,4 +154,6 @@ minor:   ${python_version:minor}     # 3.8
 micro:   ${python_version:micro}     # 3.8.2
 ```
 
+Additionally hydra supports OmegaConf <a class="external" href="https://omegaconf.readthedocs.io/en/latest/custom_resolvers.html#custom-resolvers" target="_blank">custom resolvers</a>
+
 You can learn more about OmegaConf <a class="external" href="https://omegaconf.readthedocs.io/en/latest/usage.html#access-and-manipulation" target="_blank">here</a>.