Dynamic routes clarification (#8110)
Dynamic routes clarification (#8110)

As talked in https://github.com/zeit/next.js/issues/8101 dynamic routing documentation could be confusing. This PR tries to clarify it a bit.
azukaru/next.js,zeit/next.js,JeromeFitz/next.js,flybayer/next.js,zeit/next.js,BlancheXu/test,azukaru/next.js,zeit/next.js,flybayer/next.js,BlancheXu/test,azukaru/next.js,JeromeFitz/next.js,BlancheXu/test,flybayer/next.js,azukaru/next.js,flybayer/next.js,JeromeFitz/next.js,JeromeFitz/next.js