Merge pull request #1856 from desertwitch/patch-1

en_US/helptext.txt: Fix broken link in GUI

emhttp/languages/en_US/helptext.txt

@@ -256,7 +256,7 @@ Unraid OS uses these default options when creating a multiple-device pool:
 
 `-dconvert=raid1 -mconvert=raid1`
 
-For more complete documentation, please refer to the btrfs-balance [Manpage](https://btrfs.wiki.kernel.org/index.php/Manpage/btrfs-balance)
+For more complete documentation, please refer to the btrfs-balance [Manpage](https://man7.org/linux/man-pages/man8/btrfs-balance.8.html)
 
 *Note: raid5 and raid6 are generally still considered **experimental** by the Linux community*
 :end