Fix markdownlint MD034/MD040 in notices and security docs

Wrap bare URLs and the contact email in angle brackets, and add a language to
the license-text code fences, so the shared markdown lint passes.

SECURITY.md

@@ -9,7 +9,7 @@ Please report security issues privately rather than in a public issue:
 
 - Use GitHub's "Report a vulnerability" (Security > Advisories) to open a
   private advisory, or
-- email moshe@mohome.net.
+- email <moshe@mohome.net>.
 
 Include the affected version (or `.eap` filename), camera model / Axis OS
 version, a description and its impact, and reproduction steps if available. You

THIRD_PARTY_NOTICES.md

@@ -6,15 +6,15 @@ code is licensed separately (see `LICENSE`, BSD 3-Clause).
 ## Tailscale
 
 - Copyright (c) 2020 Tailscale & AUTHORS
-- Project: https://github.com/tailscale/tailscale
+- Project: <https://github.com/tailscale/tailscale>
 - License: BSD 3-Clause
 
 Tailscale is a product of Tailscale Inc. This package independently
 redistributes the Tailscale binaries and is not affiliated with, endorsed by, or
 supported by Tailscale Inc. For the official Tailscale client, visit
-https://tailscale.com.
+<https://tailscale.com>.
 
-```
+```text
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met: