No you dont have to be muslim to be married in sharia court. Nevertheless, i think being hindu may be a problem as essentially islamic law does not recognise any other religions except christianity and judaism. You may have to check that. Converting to islam needs you to go through a process in the sharia court where you have to take an oath and you will be issued with some sort of legal document. However, i wouldnt recommend doing this just for the sake of it as technically you are swearing an oath under false pretences and that is an area where you dont want to go. I believe if you go there and say you are a christian, you will not need to produce any document.