It is important to have a License for the repository! It really helps in the long term. I believe that you just have to select the License from the predefined ones!
If you found any typo or any kind of mistake in the readme file of the repository, then feel free to raise an issue about it and improve it by creating a pull request.
Also if you want to add something new to the readme file, then do the same as I mentioned above.
I'm thinking of a feature where users can select their own background banner. To start off, you can make a few gradients selection first. On later part, users can maybe select their own plain color background with color picker.
Add a type of loading animation when we click on the create card button, so if anyone has a slow internet connection still the user gets a great experience of using the app.
How to achieve this:
Get your favorite loading animation from sites like loading.io
Display the animation when clicking on the Create Card button.
Hide animation after receiving data from GitHub API.