Create requirements.txt to simplify dependencies

[louie-github]

Hello there 😄

Keeping in mind that there are only three dependencies which are very simple to install as per the README, I'd respectfully like to suggest creating a requirements.txt file just so that people could simply shoot off a pip install -r requirements.txt.

I think the contents could be as simple as:

cssselect
lxml
requests

I'd also like to suggest changing the README to either say to simply do pip install -r requirements.txt if we do create that file, or to say pip install requests lxml cssselect if we don't create said file. It's a really simple change, but it beats having to type three commands.

Again, thank you for your work and for your time! Cheers!

[egbertbouman]

Thanks for the suggestion 👍 You're right, using a requirements..txt is more convenient. I've just added this and updated the README.