source/local: support comments in input

Lines starting with '#' are treated as comments and ignored when parsing
feature files and hook output.

docs/usage/customization-guide.md

@@ -306,13 +306,16 @@ The hook stdout and feature files are expected to contain features in simple
 key-value pairs, separated by newlines:
 
 ```plaintext
+# This is a comment
 <name>[=<value>]
 ```
 
 The label value defaults to `true`, if not specified.
 
 Label namespace may be specified with `<namespace>/<name>[=<value>]`.
 
+Comment lines (starting with `#`) are ignored.
+
 ### Mounts
 
 The standard NFD deployments contain `hostPath` mounts for

source/local/local.go

@@ -150,6 +150,11 @@ func parseFeatures(lines [][]byte) map[string]string {
 	for _, l := range lines {
 		line := strings.TrimSpace(string(l))
 		if len(line) > 0 {
+			// Skip comment lines
+			if strings.HasPrefix(line, "#") {
+				continue
+			}
+
 			lineSplit := strings.SplitN(line, "=", 2)
 
 			key := lineSplit[0]