login: add page (#4509)

pages/linux/login.md

@@ -0,0 +1,19 @@
+# login
+
+> Initiates a session for a user.
+
+- Login as a user:
+
+`login {{user}}`
+
+- Login as user without authentication if user is preauthenticated:
+
+`login -f {{user}}`
+
+- Login as user and preserve environment:
+
+`login -p {{user}}`
+
+- Login as a user on a remote host:
+
+`login -h {{host}} {{user}}`