remove the use of PHPs built-in server

[arhimede]

Since we have WSL, the PHPs built-in server is quite obsolete

Update readme.md instructions from V4

[arhimede]

let's clarify this paraghrah
https://github.com/dotkernel/frontend#testing-running
that is obsolete

** and add some text related to WSL

[alexmerlin]

Fixed in #354