Update README.md

[klppl]

Added how to find your cookies

[dgw]

Yeah, these are probably useful instructions to include, thanks for the poke. Just a couple things:

• Why are the numbered lists inside commented-out Markdown code blocks? That doesn't render properly.
• The section heading should nest under the parent heading, meaning one more # than "Configuring" has—and it could be streamlined slightly: "Getting your Twitter cookies"

[klppl]

@dgw markdown wasn't my strenght. I'll try again and make it right :)

[dgw]

You can append to this branch if you want, and I'll fix up the history before merging :)