Add 'Development' section

[riordant]

Adds an initial 'Development' section to the README, with a subsection specifying how to set up for Xcode.

[koraykoska]

Thank you. Could you also add a line which says something like:

"open Example/Web3.xcworkspace to start editing the source files of this project in XCode"

or something similar...

[riordant]

How's that? I don't know how to add symbols, maybe you could add an Xcode symbol in the title of the subsection :)

[koraykoska]

You can select one of the emojis from this list:

https://gist.github.com/rxaviers/7360908

I am afraid there is no xcode emoji, but you could select something similar...