chore: fix broken docs links (#11760)

* fixed broken install/packages.md link

* fixed broken docs links

* fixed admin/auth link

* fixed example-guide links

* replaced mitchell tweet with nix docs

* make fmt

* replaced private image with imgur

docs/admin/appearance.md

@@ -36,7 +36,7 @@ users of which network their Coder deployment is on.
 
 ## OIDC Login Button Customization
 
-[Use environment variables to customize](../auth#oidc-login-customization) the
+[Use environment variables to customize](./auth.md#oidc-login-customization) the
 text and icon on the OIDC button on the Sign In page.
 
 ## Support Links

docs/admin/configure.md

@@ -130,8 +130,8 @@ steps:
 
 ## System packages
 
-If you've installed Coder via a [system package](../install/packages.md) Coder,
-you can configure the server by setting the following variables in
+If you've installed Coder via a [system package](../install/index.md) Coder, you
+can configure the server by setting the following variables in
 `/etc/coder.d/coder.env`:
 
 ```env