doc: mention `get_read_array` and `get_write_array` in raw frame access section
doc: mention `get_read_array` and `get_write_array` in raw frame access section

They are user friendlier to use than the raw access functions.

Signed-off-by: akarin <116d91e284c519c68ed208ea7f4a4310e888fd68@users.noreply.github.com>

Kamekameha/vapoursynth,vapoursynth/vapoursynth,Kamekameha/vapoursynth,vapoursynth/vapoursynth,vapoursynth/vapoursynth,Kamekameha/vapoursynth,vapoursynth/vapoursynth,Kamekameha/vapoursynth