Base: Add manpage for groups(1)

Author: https://github.com/setepenre
Commit: 8978325af8
Pull-request: https://github.com/SerenityOS/serenity/pull/6734
Reviewed-by: https://github.com/bcoles
Reviewed-by: https://github.com/linusg

Base/usr/share/man/man1/groups.md

@@ -0,0 +1,31 @@
+## Name
+
+groups - list group memberships
+
+## Synopsis
+
+```**sh
+$ groups [username...]
+```
+
+## Description
+
+`groups` lists group memberships.
+
+If no username is provided group memberships are listed for current user.
+
+## Arguments
+
+* username: username to list group memberships for
+
+## Examples
+
+```sh
+# List group memberships for current user
+$ groups
+# List group memberships for one user
+$ groups nona
+# List group memberships for multiple users
+$ groups nona anon root
+```
+