Roadmap of detrex documentation and tutorials

[rentainhe]

We keep this issue open to collect documentation requests from users and hear your voice.

You can either:

• Suggest new documentation content or tutorial by leaving a comment.
• Vote for a documentation request with 👍. (Remember that developers are sometimes busy and cannot respond to all documentation requests, so vote for your most favorable one!)

Collection

• Custom dataset tutorial: Custom data set training using pre-trained weights #78
• Register coco-like custom dataset for training please refer to How can I use a custom dataset for training? #186

[Agito555]

Add the guidance like mmdetection to verify the installation of detrex is correct or not.