Add screenshots for all GitHub readme examples

[deltaidea]

... except for b4b4r07/dotfiles, that project has practically no readme at the time of this PR. Should probably remove it from the list.

All screenshots are 980 x 1064 == (width of GiHub layout) x (1080 display - minimal cropped header).

Please take a look at the HTML. It is good enough? I couldn't make it less verbose or translate to Markdown.
Please feel free to ignore this PR if this is not acceptable - it didn't make that much time since I managed to automate almost every step. :)

Edit: Live preview: https://github.com/deltaidea/awesome-readme/tree/screenshots

Closes #1.

[RichardLitt]

I suppose there is no way to embed the versioned screenshot of the README? Right now it links to the repository, which may not reflect the screenshot.

Let's merge the other PRs, first, and then rebase this. I'm not sure I want this, as it makes the markdown inscrutable - will depend on @matiassingers thoughts.

[deltaidea]

I suppose there is no way to embed the versioned screenshot of the README? Right now it links to the repository, which may not reflect the screenshot.

I'm not sure that you mean by that. It's possible to link to the target readme at commit at which the screenshot was made - just change the repo URL to include the current commit. Want me to do that?

[RichardLitt]

It's possible to link to the target readme at commit at which the screenshot was made - just change the repo URL to include the current commit. Want me to do that?

Exactly. That way, we won't get the issue like we had with dotfiles.

I've gone through and merged the other PRs. Mind redoing the PR? :)

[deltaidea]

Sure! Here, I've rebased the PR. Let me come up with a clever way to fetch a list of current commits for all repos.

[deltaidea]

Documented everything in contributing.md. Please review that too, as I'm not a native speaker and not completely sure how it sounds.

[RichardLitt]

Looks pretty good to me. One small nitpick.

[RichardLitt]

Follow the existing visual...

[deltaidea]

Thanks, fixed that.

[deltaidea]

This was a terrible idea because of the markup bloat.

[RichardLitt]

Well, yes and no. The implementation is very bloated.

I think one thing we could do, rather easily, is just have a link to a screenshot, and not worry about the markdown at all. Just have a [Screenshot](link) link at the end of every entry. What do you think?

[deltaidea]

Yeah, I agree.
Okay, I'll add simple links. Admittedly, they aren't nearly as usable. Gotta start somewhere though.

I could also automate taking the screenshots themselves. Would you accept something like npm run screenshots? I'd make a script that opens each repo in PhantomJS and updates the screenshot if the latest commit isn't the same as on the last run.

[RichardLitt]

That would work for me. The only issue is that we need to make sure that the screenshots match the commit of the PR, not the most recent commit in whatever given README.