[clang-tidy][NFC] Clarify switch-missing-default-case doc (#164699) (#164709)

Falling through a defaultless switch statement has well defined
behavior. Fixes #164699.

Credit for noticing this problem goes to user "pozz" on comp.lang.c,
Message-ID: <[email protected]>

Author: Keith-S-Thompson

clang-tools-extra/docs/clang-tidy/checks/bugprone/switch-missing-default-case.rst

@@ -9,8 +9,8 @@ on covering cases with non-enums where the compiler may not issue warnings.
 Switch statements without a default case can lead to unexpected
 behavior and incomplete handling of all possible cases. When a switch statement
 lacks a default case, if a value is encountered that does not match any of the
-specified cases, the program will continue execution without any defined
-behavior or handling.
+specified cases, the switch statement will do nothing and the program will
+continue execution without handling the value.
 
 This check helps identify switch statements that are missing a default case,
 allowing developers to ensure that all possible cases are handled properly.