Update README for greater consistency with styled API

[andriibieriezhnoi]

I think it would be more convenient for users who switch from styled-components

Reference #33

[ai]

Also it is a little shorter

[taion]

wait this works? @jquense why don't we use this then

[ai]

@taion yeap, @jquense added this syntax to fix my old issue #33

[jquense]

I think it's less good of a syntax personally, with styled() you use the same function call for dom elements or custom components, it's also a bit less error prone.

Happy to show it in the readme but I think we should prefer the function generally

[ai]

@jquense yeap, we can do it in a different way. We just need to explain for styled components users that they do not need to change the syntax. Do you have an idea how to do it?

[andriibieriezhnoi]

@jquense
I think astroturf should attract styled/emotion users and README will show them that migrating is not so difficult. This is why I think it is important for us to use SC syntax.

[jquense]

for sure we should show it and illustrate a migration path, I just don't think we should do so at the expense of now using the other syntax at all.

Can we add a section that shows both? and/or some copy for folks coming from SC or emotion?

[ai]

Maybe it is a good time to write a special section for Migration from SC. We can cover there:

1. Syntax difference. Show what is supported.
2. Show workaround for keyframes and injectGlobal.
3. Explain how to set constants (use postcss-custom-properties or postcss-env-function).
4. How to have dynamic parts in styles (Custom Properties).