Fix making the partition bootable instructions

[nicolaevladescu]

Motivation for this change

In util-linux 2.31.1 fdisk moved the "a" command for making a partition bootable, to "A" in expert mode.

Things done

Nothing, it's just documentation.

[matthewbauer]

This is very weird. On my system I get this:

Welcome to fdisk (util-linux 2.32.1).                                                                                                                        
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): m

Help:

  DOS (MBR)
   a   toggle a bootable flag
   b   edit nested BSD disklabel
   c   toggle the dos compatibility flag

  Generic
   d   delete a partition
   F   list free unpartitioned space
   l   list known partition types
   n   add a new partition
   p   print the partition table
   t   change a partition type
   v   verify the partition table
   i   print information about a partition

  Misc
   m   print this menu
   u   change display/entry units
   x   extra functionality (experts only)

  Script
   I   load disk layout from sfdisk script file
   O   dump disk layout to sfdisk script file

  Save & Exit
   w   write table to disk and exit
   q   quit without saving changes

  Create a new label
   g   create a new empty GPT partition table
   G   create a new empty SGI (IRIX) partition table
   o   create a new empty DOS partition table
   s   create a new empty Sun partition table

Where a is still a command in 2.32.1. Maybe the change in util-linux was reverted?

[samueldr]

Hi! Closing this issue since the partitioning instructions are now re-written for 18.09. (See #47697)