add documentation for url attribute
add documentation for url attribute

underdogio/splinter,gjvis/splinter,underdogio/splinter,underdogio/splinter,cobrateam/splinter,bubenkoff/splinter,gjvis/splinter,nikolas/splinter,bmcculley/splinter,gjvis/splinter,lrowe/splinter,bmcculley/splinter,objarni/splinter,lrowe/splinter,bmcculley/splinter,drptbl/splinter,lrowe/splinter,nikolas/splinter,myself659/splinter,nikolas/splinter,drptbl/splinter,cobrateam/splinter,myself659/splinter,myself659/splinter,bubenkoff/splinter,objarni/splinter,objarni/splinter,drptbl/splinter,cobrateam/splinter