Update getting-started.md

[nthaisieng]

Important

• If this PR updates a file in content/vi with a lastmod field, it must be updated.

• If this PR is a translation, please read https://github.com/letsencrypt/website/blob/master/TRANSLATION.md first.

[bdaehlie]

Thank you for the translation but this kind of thing needs to be done through our translation platform, Crowdin. @ludekjanda can help give pointers about it.

[ludekjanda]

@nthaisieng Here is the direct link to the German translation page on our translation platform. Once the file is completely translated and the translations are approved, the translation will be published on the website. I am active on that platform. If you need help, you can always ask me in the comments or in the discussion forum there. Thank you.