Update README.md

Fix url to readthedocs

README.md

@@ -8,7 +8,7 @@ knowledge in INDRA for network path searches. The service is available at
 [https://network.indra.bio](https://network.indra.bio).
 
 Read the 
-[documentation](https://indra_network_search.readthedocs.io/en/latest/)
+[documentation](https://indra-network-search.readthedocs.io/en/latest/)
 for more information about how to use the web ui and read the 
 [API documentation](https://network.indra.bio/api/docs) for more information 
 on the rest API.