docs: add UPCLOUD_TOKEN mentions to credential documentation (#627)

Co-authored-by: Toni Kangas <kangasta@users.noreply.github.com>

Author: mgajda

docs/index.md

@@ -223,14 +223,16 @@ On bash, the completions depend on `bash-completion` package. Install and config
 
 To be able to manage your UpCloud resources, you need to configure credentials for `upctl` and enable API access for these credentials.
 
-Define the credentials either by setting `UPCLOUD_USERNAME` and `UPCLOUD_PASSWORD` environmental variables or `UPCLOUD_TOKEN` environment variable,
-or in the `upctl` config file (default `~/.config/upctl.yaml`, overridable with `--config /path/to/upctl.yaml`):
+We recommend using API tokens for authentication. Configure credentials by using `upctl account login --with-token` command to save a token to system keyring, in the `upctl` config file (default `~/.config/upctl.yaml`, overridable with `--config /path/to/upctl.yaml`) or by setting the `UPCLOUD_TOKEN` environment variable. Alternatively, you can use `UPCLOUD_USERNAME` and `UPCLOUD_PASSWORD` environment variables:
 
 ```yaml
+# recommended: use API token
+token: "your-token"
+
+# alternatively, use username and password
 username: "your-username"
 password: "your-password"
-# alternatively, you can use token
-token: "your-token"
+```
 
 API access can be configured in the UpCloud Hub on [Account page](https://hub.upcloud.com/account/overview) for the main-account and on the [Permissions tab](https://hub.upcloud.com/people/permissions) of the People page for sub-accounts. We recommend you to set up a sub-account specifically for the API usage with its own username and password, as it allows you to assign specific permissions for increased security.
 

internal/core/core.go

@@ -23,7 +23,7 @@ const rootCmdLongDescription = `UpCloud command-line interface
 
 ` + "`" + `upctl` + "`" + ` provides a command-line interface to UpCloud services. It allows you to control your resources from the command line or any compatible interface.
 
-To be able to manage your UpCloud resources, you need to configure credentials for ` + "`" + `upctl` + "`" + ` and enable API access for these credentials. Define the credentials by setting ` + "`" + `UPCLOUD_USERNAME` + "`" + ` and ` + "`" + `UPCLOUD_PASSWORD` + "`" + ` environment variables. API access can be configured on the Account page of the UpCloud Hub. We recommend you to set up a sub-account specifically for the API usage with its own username and password, as it allows you to assign specific permissions for increased security.`
+To be able to manage your UpCloud resources, you need to configure credentials for ` + "`" + `upctl` + "`" + `. We recommend using API tokens. Configure credentials by using ` + "`" + `upctl account login --with-token` + "`" + ` command to save a token to system keyring, in ` + "`" + `~/.config/upctl.yaml` + "`" + ` or set the ` + "`" + `UPCLOUD_TOKEN` + "`" + ` environment variable. Alternatively, use ` + "`" + `UPCLOUD_USERNAME` + "`" + ` and ` + "`" + `UPCLOUD_PASSWORD` + "`" + ` environment variables. When using username and password, API access can be configured on the Account page of the UpCloud Hub. We recommend you to set up a sub-account specifically for the API usage with its own credentials, as it allows you to assign specific permissions for increased security.`
 
 // BuildRootCmd builds the root command
 func BuildRootCmd(conf *config.Config) cobra.Command {