Merge pull request hyperledger#573 from hyperledger/fix-link

Fix link in Readme

README.md

@@ -173,7 +173,7 @@ If you made changes in both indy-plenum and indy-node, you need to do the follow
     - [Request Handling](https://github.com/hyperledger/indy-plenum/blob/master/docs/request_handling.md)
     - [Catchup](https://github.com/hyperledger/indy-plenum/blob/master/docs/catchup.md)
     - [Plugins](https://github.com/hyperledger/indy-plenum/blob/master/docs/plugins.md)
-- Relationship between Entities and Transactions: [relationship diagram](docs/relationship diagram.png)
+- Relationship between Entities and Transactions: [relationship diagram](docs/relationship-diagram.png)
 - Supported transactions and their format: [transactions](docs/transactions.md)
 - Supported requests (write, read) and their format: [requests](docs/requests.md)
 - [Network roles and permissions](https://docs.google.com/spreadsheets/d/1TWXF7NtBjSOaUIBeIH77SyZnawfo91cJ_ns4TR-wsq4/edit#gid=0)