uefi: Add panic doc to uefi::helpers::init

This function may panic if called more than once, because `log::set_logger`
panics if called more than once. Document this panic.

Author: nicholasbishop

uefi/src/helpers/mod.rs

@@ -55,6 +55,10 @@ pub fn system_table() -> SystemTable<Boot> {
 /// **PLEASE NOTE** that these helpers are meant for the pre exit boot service
 /// epoch. Limited functionality might work after exiting them, such as logging
 /// to the debugcon device.
+///
+/// # Panics
+///
+/// This function may panic if called more than once.
 #[allow(clippy::missing_const_for_fn)]
 pub fn init() -> Result<()> {
     // Set up logging.