To create bows you just need to follow the tutorial here, but in step 8 you need also to copy bowX_0.json , bowX_1.json and bowX_2.json beacause these are the models of pulling bow animation.
So you can easly edit these copied files following your needs following these steps:
8.1) Copy these 3 files and replace the 0 after "bow" into your bow id you've chosen in customBows.yml
8.2) Then you just need to edit textures->layer0 attribute of these 3 json files setting them to you texture path as seen in next steps of the tutorial .
Pretty easy, right?