Expand documentation for the groups module

src/groups/mod.rs

@@ -1,4 +1,18 @@
 //! Payphone-specific code. All features like calls and moderation go here.
+//! 
+//! Sub-modules in this module usually follow the same structure:
+//! 
+//! - A `mod.rs` file exporting the public API of the sub-module.
+//! - A `commands.rs` file containing the command definitions.
+//! - A `embeds.rs` file containing embed-generating functions for those commands.
+//! - A `events.rs` file containing event handlers related to the features the sub-module covers.
+//! - Any additional modules the sub-module may specifically require.
+//! 
+//! An example of extra modules not listed above is the [`calls::moderation`] module, which
+//! includes the tools for parsing messages and detecting rule breakings in them.
+//! 
+//! > *Note that not all sub-modules have commands, nor they all have event listeners, etc. Each of
+//! > them only defines the modules they need.*
 
 pub mod about;
 pub mod calls;