Add an example for the --vmodule flag.

This makes it easier to copy-paste, without having to read the full documentation.

PiperOrigin-RevId: 670982905
Change-Id: I2f3844f30bc289053943aef3c15fdc5433203eb9

Author: Abseil Team

absl/log/absl_vlog_is_on.h

@@ -40,6 +40,8 @@
 // last . and everything after it) is stripped from each filename prior to
 // matching, as is the special suffix "-inl".
 //
+// Example: --vmodule=module_a=1,module_b=2
+//
 // Files are matched against globs in `--vmodule` in order, and the first match
 // determines the verbosity level.
 //

absl/log/vlog_is_on.h

@@ -40,6 +40,8 @@
 // last . and everything after it) is stripped from each filename prior to
 // matching, as is the special suffix "-inl".
 //
+// Example: --vmodule=module_a=1,module_b=2
+//
 // Files are matched against globs in `--vmodule` in order, and the first match
 // determines the verbosity level.
 //