apply reviewer suggestions

Co-authored-by: Andrew Lamb <[email protected]>

README.md

@@ -94,9 +94,11 @@ Planned Release Schedule
 
 In general, use panics for bad states that are unreachable, unrecoverable or harmful.
 For those caused by invalid user input, however, we prefer to report that invalidity
-gracefully as an error result instead of panicking. Note that it still makes sense
-to have some panic/assert statements, given that the invalidity of user input is
-examined and reported as errors first.
+gracefully as an error result instead of panicking. In general, invalid input should result
+in an `Error` as soon as possible. It *is* ok for code paths after validation to assume validation has 
+already occurred and and panic if not. See [this ticket] for more nuances.
+
+[this ticket]: https://github.com/apache/arrow-rs/issues/6737
 
 ### Deprecation Guidelines