More precise explanation of using LEAVE for .close

There is probably a much better way to phrase it, but for the moment
this will do.

Author: AlexDaniel

doc/Type/IO.pod6

@@ -230,7 +230,9 @@ written equivalently like so:
 
 When a file was opened for writing, closing it is important to ensure that all
 contents are actually written to the file. You may want to consider using a
-L<LEAVE|/language/phasers#LEAVE> phaser to guard against exceptions.
+L<LEAVE|/language/phasers#LEAVE> phaser to guard against exceptions in
+your code that could prevent your program from reaching the line with
+C<$fh.close>.
 
 =head2 sub slurp