fix: Mark tel: links as safe

By default, Hugo only allows using `http:`, `https:`, and `mailto:`.
URLs using other schemes are replaced with `#ZgotmplZ`.
To allow using `tel:`, we have to declare it as safe using `| safeURL`.
This marks every URL as safe which should be fine, since all content
inside the repo is trusted.
See https://gohugo.io/functions/safe/url/ for more info.

Closes #185

Author: zusorio

layouts/_default/_markup/render-link.html

@@ -2,5 +2,5 @@
 {{- if strings.HasPrefix $url "http" -}}
 {{ partial "link" . }}
 {{- else -}}
-<a href="{{ $url }}">{{ .Text }}</a>
+<a href="{{ $url | safeURL }}">{{ .Text }}</a>
 {{- end -}}