Default worker's name to hostname (#196)

* Default worker's name to hostname

* Replaced hostname term

* connected-device label in the example

PERSISTENT-WORKERS.md

@@ -8,25 +8,21 @@ Follow the instruction in the [INSTALL.md](INSTALL.md) but note that Docker or P
 
 ## Running
 
-The most simplest invocation looks like this:
+The simplest invocation looks like this:
 
 ```
 cirrus worker run --token <poll registration token>
 ```
 
 This will start the persistent worker that periodically poll for new tasks in the foreground mode.
 
-By default the worker's name gets assigned semi-automatically based on the name of the current system and a counter variable. Specify `--name` to explicitly specify the worker's name:
+By default, the worker's name is equal to the name of the current system. Specify `--name` to explicitly provide the worker's name:
 
 ```
 cirrus worker run --token <poll registration token> --name z390-worker
 ```
 
-Note that persistent worker's name should be unique within a poll, otherwise a registration will fail. To avoid this, use a special counter variable `%n` that gets expanded in the cloud to the worker's registration slot:
-
-```
-cirrus worker run --token <poll registration token> --name "z390-worker-%n"
-```
+Note that persistent worker's name should be unique within a pool.
 
 ## Configuration
 
@@ -37,20 +33,22 @@ Example configuration:
 ```yaml
 token: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
 
-name: "%hostname-%n"
+name: "MacMini-Slot-1"
 
 labels:
-  distro: debian
+  connected-device: iPhone12ProMax
 ```
 
-Currently configuration files support the same set of options exposed via the command-line flags, but in the future the only way to configure certain options would be using the configuration file.
+Currently, configuration files support the same set of options exposed via the command-line flags, but in the future the only way to configure certain options would be using the configuration file.
 
 ## Writing tasks
 
 Here's an example of how to run a task on one of the persistent workers [registered in the dashboard](https://cirrus-ci.com/):
 
 ```yaml
 task:
-  persistent_worker: {}
+  persistent_worker:
+    labels:
+      os: darwin
   script: echo "running on-premise"
 ```

internal/commands/worker/run.go

@@ -6,6 +6,7 @@ import (
 	"github.com/cirruslabs/cirrus-cli/internal/worker"
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
+	"os"
 )
 
 var ErrRun = errors.New("run failed")
@@ -60,7 +61,8 @@ func NewRunCmd() *cobra.Command {
 
 	cmd.PersistentFlags().StringVarP(&configPath, "file", "f", "", "configuration file path (e.g. /etc/cirrus/worker.yml)")
 
-	cmd.PersistentFlags().StringVar(&name, "name", "%hostname-%n", "worker name to use when registering in the pool")
+	hostname, _ := os.Hostname()
+	cmd.PersistentFlags().StringVar(&name, "name", hostname, "worker name to use when registering in the pool")
 	_ = viper.BindPFlag("name", cmd.PersistentFlags().Lookup("name"))
 
 	cmd.PersistentFlags().StringVar(&token, "token", "", "pool registration token")