Fixed a few formatting errors and updated

Added immutable v mutable, but unsure where to put it so I'll leave that up to you. Fixed some formatting errors where the '```' needs to be put at the beginning of the line for it to take effect properly otherwise the blocks say objective-c at the start and dont have word colouring etc.
Merge pull request #1 from Nicrob64/patch-1

Fixed a few formatting errors and updated