doc: Add a trivial example
doc: Add a trivial example

sdac/httprouter,glycerine/httprouter,buaazp/fasthttprouter,cmars/tools,cmars/tools,herzog31/httprouter,cmars/tools,nigeldunn/httprouter,yosssi/httprouter,hawx/route,hiteshjoshi/httprouter,jjeffery/httprouter,TheHippo/httprouterc,b54898533/httprouter,kingland/httprouter,julienschmidt/httprouter,agaurav/httprouter,cmars/tools,EricLagergren/httprouter,Pacoup/httprouter,laurennicoleroth/httprouter