Better wordings on section intro

Co-authored-by: Alex-Welsh <[email protected]>

Author: seunghun1ee

doc/source/configuration/vault.rst

@@ -113,7 +113,7 @@ Certificates generation
 Create the external TLS certificates (testing only)
 ---------------------------------------------------
 
-This method should only be used for testing. For external certificates on production system,
+This method should only be used for testing. For external TLS on production systems,
 See `Installing External TLS Certificates <installing-external-tls-certificates>`__.
 
 Typically external API TLS certificates should be generated by a organisation's trusted internal or third-party CA.