buildcfg.rs: improve doc

src/buildcfg.rs

@@ -1,5 +1,16 @@
+//! Exports configuration data from the build system
+
+/// The configured configuration directory
 pub const CONFIGDIR: &'static str = env!("PROXMOX_CONFIGDIR");
 
+/// Prepend configuration directory to a file name
+///
+/// This is a simply way to get the full path for configuration files.
+/// #### Example:
+/// ```
+/// # #[macro_use] extern crate proxmox_backup;
+/// let cert_path = configdir!("/proxy.pfx");
+/// ```
 #[macro_export]
 macro_rules! configdir {
     ($subdir:expr) => (concat!(env!("PROXMOX_CONFIGDIR"), $subdir))