docs: update release footer

Author: reddec

_footer.md

@@ -1,6 +1 @@
-For Ubuntu/Debian (should be for all LTS)
-
-```bash
-sudo wget -O trusted-cgi_0.3.7_linux_amd64.deb https://github.com/reddec/trusted-cgi/releases/download/v0.3.7/trusted-cgi_0.3.7_linux_amd64.deb
-sudo apt install ./trusted-cgi_0.3.7_linux_amd64.deb
-```
+See [installation manual](https://trusted-cgi.reddec.net/administrating/installation/)