sample config: add S3 public endpoint option

lib/mix/tasks/sample_config.eex

@@ -25,18 +25,21 @@ config :pleroma, Pleroma.Repo,
   hostname: "localhost",
   pool_size: 10
 
-# Configure S3 support if desired:
+# Configure S3 support if desired.
+# The public S3 endpoint is different depending on region and provider,
+# consult your S3 provider's documentation for details on what to use.
 #
 # config :pleroma, Pleroma.Upload,
 #   use_s3: true,
-#   bucket: "some-bucket"
+#   bucket: "some-bucket",
+#   public_endpoint: "https://s3.amazonaws.com"
 #
 # Configure S3 credentials:
 # config :ex_aws, :s3,
 #   access_key_id: "xxxxxxxxxxxxx",
 #   secret_access_key: "yyyyyyyyyyyy",
 #   region: "us-east-1",
-#   scheme: "https://",
+#   scheme: "https://"
 #
 # For using third-party S3 clones like wasabi, also do:
 # config :ex_aws, :s3,