Add documentation

[filips123]

Add documentation, examples and README file about this project. So it will be easier to use it.

[keradus]

Can you please propose one, @filips123 ?

[filips123]

I will try if I will have time. Can you explain to me how this package work so I can add this to documentation?

[keradus]

aliases of renamed classes + adding missing methods that were created in newer version of PHPUnit.
package is super small, just check the content of it ;)

for small package that is using polyfill (except of big PHP CS Fixer repo) - see https://github.com/PHPUnitGoodPractices/Traits/search?q=polyfill&unscoped_q=polyfill