Fix documentation of the enable_service_account_auth flag.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=123666355

Author: b-daniels

README.md

@@ -134,7 +134,7 @@ _Option A_: add this code to the beginning of your `main()` function:
 try:
   import googleclouddebugger
   googleclouddebugger.AttachDebugger(
-      enable_service_account=True,
+      enable_service_account_auth=True,
       project_id='my-gcp-project-id',
       project_number='123456789',
       service_account_email='123@developer.gserviceaccount.com',