Upated some instructions

[NollKollTroll]

Updated the instructions to fit better with my experience assembling the PCB. I hope this PR is correctly done.

[thejpster]

There's another picture of the audio header in the section Not using a PCB Case. Could we make them look similar (albeit one has the jumpers indicated)?

[thejpster]

Maybe also add a note "See Not using a PCB Case if you don't actually connect this header to your ATX case, as you'll need to fit some jumpers". Or similar words.

[NollKollTroll]

Will do, great addition!

[NollKollTroll]

Updated regarding jumpers.

[thejpster]

Thank you! :)