add requiremetn for readthedoc build
add requiremetn for readthedoc build


Former-commit-id: dddb60a932cffe30ba8035e4cd5d7b50e6e3280f [formerly 55849f6d1d396af6ea6279beb81105adfafa9f0c] [formerly d9d331e462b40bcb8049da119f7b51b224b0690b]
Former-commit-id: 9b796d9faf7f81f92586a6ad89c092399e4071a7
Former-commit-id: d87e469c2e8c0ff5db04a5d8614e83013cd3060a
cthorey/pdsimage