Adding link to related sovrin-sip.

Signed-off-by: Richard Esplin <[email protected]>

text/0162-plugin-removal-helpers/README.md

@@ -13,7 +13,7 @@ In this HIPE, we propose two new features for Indy Node that will assist with re
 
 ## Motivation
 
-Indy Plenum can be extended through the use of [ledger plugins](https://github.com/hyperledger/indy-plenum/blob/master/docs/source/plugins.md). Ledger plugins can introduce new transaction types that are either stored on existing ledgers, or on new ledgers created by the plugins. The [Sovrin Network](http://sovrin.org) used this capability to develop a [token plugin for Indy](https://github.com/sovrin-foundation/token-plugin) that stored fee and value transfer transactions on a token ledger. After experimenting with the plugin, [they decided to remove it]().
+Indy Plenum can be extended through the use of [ledger plugins](https://github.com/hyperledger/indy-plenum/blob/master/docs/source/plugins.md). Ledger plugins can introduce new transaction types that are either stored on existing ledgers, or on new ledgers created by the plugins. The [Sovrin Network](http://sovrin.org) used this capability to develop a [token plugin for Indy](https://github.com/sovrin-foundation/token-plugin) that stored fee and value transfer transactions on a token ledger. After experimenting with the plugin, [they decided to remove it](https://github.com/sovrin-foundation/sovrin-sip/tree/master/text/5005-token-removal/README.md).
 
 Removing the plugin has three important consequences:
 * The data stored on the custom ledger created by the plugin will be deleted.