Explain purpose of VulnerabilityHumanEncoding

adds a go doc explaining the purpose of the map containing mapping from
int encoded state to human friendly strings

Signed-off-by: Michal Wasilewski <mwasilewski@gmx.com>

sysfs/vulnerability.go

@@ -36,6 +36,8 @@ const (
 )
 
 var (
+	// VulnerabilityHumanEncoding allows mapping the vulnerability state (encoded as an int) onto a human friendly
+	// string. It can be used by consumers of this library to expose to the user the state of the vulnerability.
 	VulnerabilityHumanEncoding = map[int]string{
 		VulnerabilityStateNotAffected: notAffected,
 		VulnerabilityStateVulnerable:  vulnerable,