This shows the bare minimum on how to flash your Pinecil with custom/new firmware, as well as changing things like the boot logo.
NOTE: This guide should work on both Linux and macOS as is, however it has only been tested on macOS Big Sur 11.6, so some steps might differ slightly on Linux, at least at the time of writing this.
The following dependencies are necessary for the entirety of the guide, however here we are only showing how to install them on macOS.