docs: document GDPR compliant

Fixes #7

docs/gdpr.md

@@ -1,6 +1,10 @@
 # Why redir is GDPR compliant?
 
-TODO
+There are several features are supported for GDPR:
+
+1. It is possible to hide IP addresses from collected access statistics
+2. Public pages provides imprint (/s/.impressum), privacy (/s/.privacy), and contact (/s/.contact) pages. The content of all these pages can be customized.
+3. When shortening a link, it is possible to set if a link is trustable or not. Any external domain links are by default untrusted. A configured trusted link will do direct redirects, and untrusted links will show a warning page to visitors then explicitly ask for permission of redirect.
 
 ## License