Append new/unknown packages from included files (#165)

This way you can include additional packages from a different source and
the main global.toml doesn't need to be aware of which packages you
might want to include, the only reference to the include is in the
local.toml.

src/config.rs

@@ -282,10 +282,8 @@ fn merge_configuration_files(
             }
 
             if !included.is_empty() {
-                anyhow::bail!(
-                    "unknown packages: {:?}",
-                    included.keys().cloned().collect::<Vec<_>>()
-                );
+                debug!("append unknown packages: {:?}", included.keys());
+                global.packages.append(&mut included);
             }
 
             Ok(())