Lets use the proper term legal notice

From wikipedia https://en.wikipedia.org/wiki/Impressum:
The terms "masthead" and "colophon" apply to printed publications only
and are not commonly used on English-language websites, while "site
notice" is website-specific and "legal notice" or "legal disclosure" are
rarely found in printed works. An "imprint" in publishing may also mean
a brand name under which a work is published,[6] and so may not be
understood to mean an Impressum.

Signed-off-by: Artem Sidorenko <artem@posteo.de>

Author: artem-sidorenko

content/imprint.md

@@ -0,0 +1,6 @@
+---
+title: "Legal Notice"
+layout: legal
+aliases:
+  - /imprint/
+---

content/legal.md

@@ -1,5 +1,5 @@
 <ul>
-  <li><a href="/imprint">Imprint</a></li>
+  <li><a href="/legal">Legal notice</a></li>
   <li><a href="/contributing">Contributing</a></li>
   <li><a href="https://twitter.com/devsecio">Twitter</a></li>
   <li><a href="https://gitter.im/dev-sec/general?source=orgpage">Gitter</a></li>