grub/help/en_US: Fix typos (#2024)

* grub/help/en_US: Fix typos

* Apply suggestions from code review

* Fix typo in line 15

INSTALL/grub/help/en_US.txt

  L - Language Select
-F1 - Display this help information
-F2 - Browse and boot files in local disk
+F1 - Display help information
+F2 - Browse and boot files in the local disk
 F3 - Switch menu mode between Treeview <-> ListView
-F4 - Boot Windows/Linux in local disk
+F4 - Boot Windows/Linux on the local disk
 F5 - Utilities
 F6 - Load Custom Grub2 Menu
 F7 - Switch between GUI Mode <-> TEXT Mode
@@ -11,8 +11,8 @@ m/Ctrl+m - Checksum image files (md5/sha1/sha256/sha512)
 d/Ctrl+d - Memdisk Mode (Only for small WinPE/LiveCD ISO/IMG)
 w/Ctrl+w - WIMBOOT Mode (Only for standard Windows ISO)
 r/Ctrl+r - Grub2 Mode (Only for some Linux distros)
-i/Ctrl+i - Compatible Mode (Just only for debug)
-u/Ctrl+u - Load ISO efi driver (Just only for debug, can not be used officially)
+i/Ctrl+i - Compatible Mode (Only for debugging)
+u/Ctrl+u - Load ISO EFI driver (Only for debugging, cannot be used officially)