add example releases.conf and skip _-prefixed dirs in fetchraw

The discover() function now skips directories starting with _ (like
_example, _webi, _common) so infrastructure dirs aren't treated as
packages to fetch.

_example/releases.conf

@@ -0,0 +1,5 @@
+# Example releases.conf — uses ripgrep as a sample project.
+# Copy this file into your package directory and adjust.
+source = github
+owner = BurntSushi
+repo = ripgrep

cmd/fetchraw/main.go

@@ -105,6 +105,10 @@ func discover(dir string) ([]pkgConf, error) {
 	var packages []pkgConf
 	for _, path := range matches {
 		name := filepath.Base(filepath.Dir(path))
+		// Skip infrastructure dirs (_example, _webi, _common, etc.)
+		if strings.HasPrefix(name, "_") {
+			continue
+		}
 		conf, err := installerconf.Read(path)
 		if err != nil {
 			log.Printf("warning: %s: %v", path, err)