Add dev installation section

[G07cha]

Guide to setup app for development but for now I've expecting issue when using npm start command.

Please, don't merge it until #7 don't be fixed

[rhysd]

Did you really try this sequence? I think rake build is needed to compile TypeScript codes. Please confirm that the sequence succeeds at least in your environment before sending pull request.

[G07cha]

As I mentioned here is an issue #7 that blocks following guide, I'll try rake build and if it succeed we have 2 options. Update guide or update package.json file.

[G07cha]

Find the way to run app, it requires tsd module installed globally and as you said compiled TypeScript. Should we add preinstall hook to package.json?

[rhysd]

OK, I'll write instruction to README. Could you check it?

[G07cha]

Sure, I also can update this pr with correct instruction.

[rhysd]

I wrote.

https://github.com/rhysd/Trendy#development

Could you try this?

[G07cha]

Yep, It's correct.

[rhysd]

Thank you for the confirmation. It was helpful.

[G07cha]

You are welcome.