BREAKING: Interface name is now specified by configuration file

The syntax for the hypd server command has changed.  Now instead of specifying an interface name as an argument to the server command, you instead specify a configuration file path.

Example:
./hypd server hypdconfig.json

hypd/configuration/configuration.go

@@ -7,6 +7,7 @@ import (
 )
 
 type HypdConfiguration struct {
+	NetworkInterface      string `json:"networkInterface"`
 	PreSharedKeyDirectory string `json:"preSharedKeyDirectory"` // hypd will load all *.secret files from this directory
 	SuccessAction         string `json:"successAction"`         // The action to take
 	TimeoutSeconds        int    `json:"timeoutSeconds"`        // If > 0, once a knock sequence has been successful this value will count down and when it reaches 0, it will perform the TimeoutAction on the client.
@@ -19,6 +20,7 @@ type HypdConfiguration struct {
 func LoadConfiguration(configFilePath string) (*HypdConfiguration, error) {
 	if configFilePath == "" {
 		commonLocations := []string{"hypdconfig.json",
+			"~/.hypdconfig.json",
 			"~/.config/hyp/hypdConfig.json",
 			"/etc/hyp/hypdConfig.json",
 			"/usr/local/etc/hyp/hypdConfig.json",
@@ -33,6 +35,7 @@ func LoadConfiguration(configFilePath string) (*HypdConfiguration, error) {
 	}
 	// if it's still not found after checking common locations, load default config
 	if configFilePath == "" {
+		fmt.Println("no configuration file found.  You can generate one with ./hypd generate defaultconfig | tee hypdconfig.json")
 		return DefaultConfig(), nil
 	}
 
@@ -45,17 +48,18 @@ func LoadConfiguration(configFilePath string) (*HypdConfiguration, error) {
 		return nil, fmt.Errorf("failed to read config file '%s': %w", configFilePath, err)
 	}
 
-	var hypdConfiguration *HypdConfiguration
+	hypdConfiguration := &HypdConfiguration{}
 	err = json.Unmarshal(b, hypdConfiguration)
 	if err != nil {
 		return nil, fmt.Errorf("failed to unmarshal config file json to HypdConfiguration (is the config file malformed?): %w", err)
 	}
 
-	return nil, nil
+	return hypdConfiguration, nil
 }
 
 func DefaultConfig() *HypdConfiguration {
 	return &HypdConfiguration{
+		NetworkInterface:      "enp0s3",
 		PreSharedKeyDirectory: "./secrets/",
 		SuccessAction:         "iptables -A INPUT -p tcp -s %s --dport 22 -j ACCEPT",
 		TimeoutSeconds:        1440,