fix links in tails sysadmins doc home page

These is the content that still lives here for now:

- [[how-tos]]

- [[processes]]

- [[providers]]

- [[role-description]]

- [[services]]

- [[scripts]]

- [[tails/how-tos]]

- [[tails/processes]]

- [[tails/providers]]

- [[tails/role-description]]

- [[tails/services]]

- [[tails/scripts]]

Note: this wiki also contains non-markdown file, clone the corresponding repo

to see them.