Add contracts submodule

This is required in order to generate the balenaOS contracts used in
release deployments.

Change-type: patch
Signed-off-by: Alex Gonzalez <alexg@balena.io>

Author: alexgg

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "balena-yocto-scripts"]
 	path = balena-yocto-scripts
 	url = https://github.com/balena-os/balena-yocto-scripts.git
+[submodule "contracts"]
+	path = contracts
+	url = https://github.com/balena-io/contracts.git

contracts

@@ -6,3 +6,5 @@ upstream:
     url: 'http://github.com/balena-os/meta-balena'
   - repo: 'balena-yocto-scripts'
     url: 'http://github.com/balena-os/balena-yocto-scripts'
+  - repo: 'contracts'
+    url: 'https://github.com/balena-io/contracts.git'