add missing information

It's important to note this env var needs to be organization ID, at least for individual users (organization name doesn't work).

website/source/docs/providers/scaleway/index.html.markdown

@@ -91,6 +91,6 @@ provider "scaleway" {
 
 ...and instead set these environment variables:
 
-- **SCALEWAY_ORGANIZATION**: Your Scaleway organization
+- **SCALEWAY_ORGANIZATION**: Your Scaleway organization ID
 - **SCALEWAY_ACCESS_KEY**: Your API Access key
 - **SCALEWAY_REGION**: The Scaleway region