gcloud: add CLI example (#1808)

docs/content/dns/zz_gen_gcloud.md

@@ -23,9 +23,16 @@ Configuration for [Google Cloud](https://cloud.google.com).
 - Since: v0.3.0
 
 
-{{% notice note %}}
-_Please contribute by adding a CLI example._
-{{% /notice %}}
+Here is an example bash command using the Google Cloud provider:
+
+```bash
+GCE_PROJECT="gc-project-id" GCE_SERVICE_ACCOUNT_FILE="/path/to/svc/account/file.json" lego \
+    --email="abc@email.com" \
+    --domains="example.com" \
+    --dns="gcloud" \
+    --path="${HOME}/.lego" \
+    run
+```
 
 
 

providers/dns/gcloud/gcloud.toml

@@ -4,7 +4,14 @@ URL = "https://cloud.google.com"
 Code = "gcloud"
 Since = "v0.3.0"
 
-Example = ''''''
+Example = '''
+GCE_PROJECT="gc-project-id" GCE_SERVICE_ACCOUNT_FILE="/path/to/svc/account/file.json" lego \
+    --email="abc@email.com" \
+    --domains="example.com" \
+    --dns="gcloud" \
+    --path="${HOME}/.lego" \
+    run
+'''
 
 [Configuration]
   [Configuration.Credentials]