The striker was signed from Evostick League One side Romulus after impressing in trials and has been given a scholarship with the Sky Blues.
Speaking to the CT, Rioch said: "He's done very well over the last four weeks and we are delighted to bring him to the club.
"He's a goal scorer who holds the ball up well, brings others into play and is quick as well.
"He can work down the sides, receives the ball well and gets into the box and provides something a little bit different to what we have got, so he will be a good addition to the group."
Richards is expected to be in the squad to face Chelsea tomorrow.