Remove git add . line

[Melesegithub]

From cyf-weather created by SallyMcGrath: CodeYourFuture/cyf-weather#41

I have banned the use of git add . at CodeYourFuture because trainees get in a huge mess not knowing what they are committing and creating gigantic unreadable diffs.

So maybe let's git add the exact file in these instructions.