add config to readme, update error output in switch command

Author: hertg

README.md

@@ -97,6 +97,39 @@ Use "egpu-switcher [command] --help" for more information about a command.
 
 ---
 
+## Configuration
+
+The config file is created automatically and can be found at `/etc/egpu-switcher/config.yaml`.
+Below you can see an example of a configuration file, annotated with some notes.
+
+```yaml
+# the 'egpu' config is generated by 'egpu-switcher config'.
+# you probably shouldn't change this manually.
+egpu:
+    driver: amdgpu
+    id: 1153611719250962689
+
+# OPTIONAL: how many times 'egpu-switcher switch auto' should retry finding the egpu.
+# this can be helpful if the egpu takes some time to connect on your machine,
+# the following values are the default, if this config is omitted.
+detection:
+  retries: 6
+  interval: 500 # milliseconds
+
+# OPTIONAL: if you want to execute a script after switching to egpu/internal.
+# the values must be absolute paths to a shell script, this script will
+# then be run with '/bin/sh $script'.
+# 
+# it is required that the script is owned by root (uid 0) 
+# and has a permission of -rwx------ (0700), in order to
+# prevent potential privilege escalation.
+hooks:
+  internal: /home/michael/tmp/internal.sh
+  egpu: /home/michael/tmp/egpu.sh
+```
+
+---
+
 ## Troubleshooting
 
 If you run into problems, please have a look at

cmd/switch.go

@@ -154,7 +154,7 @@ func switchInternal() error {
 	}
 	if post := viper.GetString("hooks.internal"); post != "" {
 		if err := runHook(post); err != nil {
-			logger.Error("egpu hook error: %s", err)
+			logger.Error("internal hook error: %s", err)
 		}
 	}
 	return nil
@@ -174,7 +174,7 @@ func switchAuto(gpu *pci.GPU) error {
 
 func runHook(script string) error {
 	if !permissionCheck(script) {
-		return fmt.Errorf("hook scripts need to be sufficiently protected because they are run as root")
+		return fmt.Errorf("hook %s will not be executed", script)
 	}
 	cmd := exec.Command("/bin/sh", script)
 	err := cmd.Run()
@@ -187,7 +187,7 @@ func runHook(script string) error {
 func permissionCheck(file string) bool {
 	info, err := os.Stat(file)
 	if err != nil {
-		logger.Debug("unable to get info about %s: %s", file, err)
+		logger.Error("%s", err)
 		return false
 	}
 	if stat, ok := info.Sys().(*syscall.Stat_t); ok {