To get started with developing Sileo you must follow a few extra steps rather than just pulling and opening the workspace.
First start by running:
git clone --recursive https://github.com/Sileo/Sileo.git
Once you do this continue by installing the Cocoapods we use:
pod install
If you do not have Cocoapods installed you can follow instructions here to do so: https://guides.cocoapods.org/using/getting-started.html
If you are too lazy to click a link, the simplest way to install Cocoapods is by running:
sudo gem install cocoapods
This should install all the pods we use along with the submodule for the LNPopupController.
Open the SileoApp.workspace not the .xcproj. Once you open the Workspace, change the Bundle ID for the Sileo project to a new identifier. This way you will be able to compile with your provisioning profile.
Good luck, if you have any questions ask a dev in the Sileo Discord Chat.