added link to CMV's wiki page Building Custom Widgets
added link to CMV's wiki page Building Custom Widgets

Updated 'Contributing to the Project' section under 'User Contributed Widgets' with a with link referencing the CMV wiki page Building Custom Widgets.
ValueCreation/cmv-app,tduerkop/cmv-app,coshx/cmv-app,dyh333/cmv-app,tduerkop/cmv-app,etes/ConfigurableViewerJSAPI,dyh333/cmv-app,gavinr/cmv-app,roemhildtg/cmv-app,coshx/cmv-app,ValueCreation/cmv-app,fileunderjeff/cmv-app,cmv/cmv-app,gavinr/cmv-app,kcsgisRham/cmv-app,roemhildtg/cmv-app,kcsgisRham/cmv-app,cmv/cmv-app,ebonan/cmv-app,tmcgee/cmv-app,ebonan/cmv-app,fileunderjeff/cmv-app,tmcgee/cmv-app,gdherbert/cmv-app,gdherbert/cmv-app