Fix documentation link in Basic API routes example (#11671)
Fix documentation link in Basic API routes example (#11671)

Link to description of API Routes in the main README of the repo is broken. Replaced with a link to the documentation.
flybayer/next.js,JeromeFitz/next.js,flybayer/next.js,azukaru/next.js,zeit/next.js,zeit/next.js,JeromeFitz/next.js,zeit/next.js,azukaru/next.js,JeromeFitz/next.js,azukaru/next.js,flybayer/next.js,azukaru/next.js,flybayer/next.js,JeromeFitz/next.js