Rocketbook Mini Pen Holder

I modified [this](https://www.printables.com/model/149728/files) pen holder model to fit my Rocketbook mini, ensuring less intrusion and accommodating various pen types. It's modeled to hold the pen along the left side, but can be mirrored along the x-axis to go on the right. I put it in front of the back cover for convenient access, but you can really put it anywhere. I printed it with a brim and supports, although they may not be necessary.