doc:add images to doc

docs/user/images/degrad_space.png

docs/user/images/dicho.png

docs/user/images/dm_degrad_temp.png

docs/user/images/dm_delay.png

docs/user/images/dm_reconfig.png

docs/user/images/dm_renounce.png

docs/user/images/fb_degrad_space.png

docs/user/images/fb_degrad_temp.png

docs/user/images/fb_delay.png

docs/user/images/fb_reconfig.png

docs/user/images/fb_renounce.png

docs/user/images/replay_rigid.png

docs/user/images/routine_greedy.png

docs/user/images/thinktimeonly.png

docs/user/user_categories.md