Improve docs for File.delete exceptions.

https://github.com/ruby/ruby/pull/1505

  Patch by @mrtazz [fix GH-1505]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60274 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

file.c

@@ -2883,6 +2883,12 @@ unlink_internal(const char *path, VALUE pathv, void *arg)
  *
  *  Deletes the named files, returning the number of names
  *  passed as arguments. Raises an exception on any error.
+ *  Since the underlying implementation relies on the
+ *  <code>unlink(2)</code> system call, the type of
+ *  exception raised depends on its error type (see
+ *  https://linux.die.net/man/2/unlink) and has the form of
+ *  e.g. <code>Errno::ENOENT</code>.
+ *
  *  See also <code>Dir::rmdir</code>.
  */