Add server-side redirect from root to real content (#1721)

Author: rjbeers

static/_redirects

@@ -519,3 +519,6 @@ https://0-13-0.docs.pomerium.io/ https://0-13-0.docs.pomerium.com/:splat 301!
 https://0-12-0.docs.pomerium.io/ https://0-12-0.docs.pomerium.com/:splat 301!
 https://0-11-0.docs.pomerium.io/ https://0-11-0.docs.pomerium.com/:splat 301!
 https://0-10-0.docs.pomerium.io/ https://0-10-0.docs.pomerium.com/:splat 301!
+
+# Avoid the index flicker in the browser
+/ /docs