Update csvjoin.rst
Update csvjoin.rst

Added an example for csvjoin.rst
doganmeh/csvkit,moradology/csvkit,jpalvarezf/csvkit,wireservice/csvkit,archaeogeek/csvkit,haginara/csvkit,arowla/csvkit,elcritch/csvkit,Tabea-K/csvkit,aequitas/csvkit,unpingco/csvkit,wjr1985/csvkit,gepuro/csvkit,nriyer/csvkit,Jobava/csvkit,kyeoh/csvkit,dannguyen/csvkit,bradparks/csvkit__query_join_filter_CSV_cli,onyxfish/csvkit,matterker/csvkit,KarrieK/csvkit,themiurgo/csvkit,tlevine/csvkit,bmispelon/csvkit,reubano/csvkit,snuggles08/csvkit,barentsen/csvkit