docs: add more doc strings

src/config.rs

@@ -7,6 +7,7 @@ use std::fs::{File, create_dir_all};
 const CONFIG_FILE_NAME:  &'static str = "tek.toml";
 const PROJECT_FILE_NAME: &'static str = "project.toml";
 
+/// Filesystem locations of things.
 pub struct AppPaths {
     config_dir:   PathBuf,
     config_file:  PathBuf,
@@ -49,6 +50,7 @@ impl AppPaths {
     }
 }
 
+/// Appears on first run (i.e. if state dir is missing).
 pub struct SetupModal(pub Option<Arc<XdgApp>>, pub bool);
 
 render!(SetupModal |self, buf, area| {