First, thank you for contributing!
When submitting new LOLs, please submit a yml sourcefile (yml/) as these are used to generate everything else. Next, review README.md and ensure that your LOL meets the criteria--interesting or unexpected functionality that would be useful to an attacker.
There's nothing special about the format. Just base your entry off an existing one and modify as required. Please ensure that you do not add or remove any of the fields; all are required.
There is a template that can be used located here if you do not want to copy one of the existing LOLs: https://github.com/LOLBAS-Project/LOLBAS/blob/master/YML-Template.yml
It is also important to use these (https://github.com/LOLBAS-Project/LOLBAS/blob/master/CategoryList.md) categories, since they relate to the web portal and it is crucial to get them right for everything to work.
Looking forward for your contributions.