add credentials sample file and ignore the actual one

.gitignore

@@ -28,3 +28,5 @@ build/Release
 # https://docs.npmjs.com/misc/faq#should-i-check-my-node-modules-folder-into-git
 node_modules
 
+# OVH credentials
+credentials.json

credentials.sample.json

@@ -0,0 +1,4 @@
+{
+  "key": "your-api-key",
+  "secret": "your-api-secret"
+}