add missing page (celo-org#157)

* add missing page

* Update sidebars.js

* Update contracts-wrappers-registry.md

Author: critesjosh

docs/developer-resources/contractkit/contracts-wrappers-registry.md

@@ -29,7 +29,7 @@ const receipt = await tx.waitReceipt()
 To interact with cUSD, is the same but with a different contract:
 
 ```ts
-const stabletoken = await kit.contract.getStableToken()
+const stabletoken = await kit.contracts.getStableToken()
 ```
 
 ## Interacting with Other Celo Contracts

sidebars.js

@@ -160,6 +160,7 @@ module.exports = {
           items: [
             'developer-resources/contractkit/index',
             'developer-resources/contractkit/setup',
+            'developer-resources/contractkit/usage',
             'developer-resources/contractkit/notes-web3-with-contractkit',
             'developer-resources/contractkit/contracts-wrappers-registry',
             'developer-resources/contractkit/odis',