docs: clarify and refine PUT vs PATCH explanation

node.js/cds-serve.md

@@ -406,14 +406,13 @@ Be aware that using an absolute path will disallow serving the service at multip
 
 ### PATCH vs. PUT vs. Replace
 
-The HTTP method `PATCH` is meant for partial modification of an _existing resource_.
-`PUT`, on the other hand, is meant for ensuring a resource exists
-, that is, if it doesn't yet exists, it gets created.
-If it does exist, it gets updated to reflect the request's content.
+The HTTP method `PATCH` is meant for partial modification of an _existing resource_.
+`PUT`, on the other hand, ensures a resource exists: a missing resource gets created,
+while an existing one gets updated with the request's content.
 
 This content, however, may be incomplete.
-By default, the values for not listed keys are not touched.
-The rationale being that default values are known and clients have the option to send full representations, if necessary.
+By default, the values for not listed fields are not touched.
+The rationale is that default values are known and clients have the option to send full representations, if necessary.
 
 The following table shows the Node.js runtime's configuration options and their respective default value: