Improve "Command-line Completion" section

Replaced deprecated Spring CLI options with the current ones,
improved section related to completion setup for zsh.

See gh-42091

Author: Alchemik

spring-boot-project/spring-boot-docs/src/docs/asciidoc/getting-started/installing.adoc

@@ -167,15 +167,15 @@ If you are on a Mac and use https://www.macports.org/[MacPorts], you can install
 [[getting-started.installing.cli.completion]]
 ==== Command-line Completion
 The Spring Boot CLI includes scripts that provide command completion for the https://en.wikipedia.org/wiki/Bash_%28Unix_shell%29[BASH] and https://en.wikipedia.org/wiki/Z_shell[zsh] shells.
-You can `source` the script (also named `spring`) in any shell or put it in your personal or system-wide bash completion initialization.
-On a Debian system, the system-wide scripts are in `<installation location>/shell-completion/bash` and all scripts in that directory are executed when a new shell starts.
+You can `source` the script named `spring` (`_spring` for zsh) or put it in your personal or system-wide bash completion initialization.
+On a Debian system, the system-wide scripts are in `<installation location>/shell-completion/<bash|zsh>` and all scripts in that directory are executed when a new shell starts.
 For example, to run the script manually if you have installed by using SDKMAN!, use the following commands:
 
 [source,shell,indent=0,subs="verbatim"]
 ----
 	$ . ~/.sdkman/candidates/springboot/current/shell-completion/bash/spring
 	$ spring <HIT TAB HERE>
-	  grab  help  jar  run  test  version
+	  encodepassword  help  init  shell  version
 ----
 
 NOTE: If you install the Spring Boot CLI by using Homebrew or MacPorts, the command-line completion scripts are automatically registered with your shell.