Update list of subdomain takeover write-ups.

There are some fantastic subdomain takeover resources out there that are worthy of a mention on this project.

README.md

@@ -11,7 +11,11 @@
 ## What is a sub-domain takeover?
 > Subdomain takeover vulnerabilities occur when a subdomain (subdomain.example.com) is pointing to a service (e.g. GitHub pages, Heroku, etc.) that has been removed or deleted. This allows an attacker to set up a page on the service that was being used and point their page to that subdomain. For example, if subdomain.example.com was pointing to a GitHub page and the user decided to delete their GitHub page, an attacker can now create a GitHub page, add a CNAME file containing subdomain.example.com, and claim subdomain.example.com.
 
-You can read up more about subdomain takeovers here: https://labs.detectify.com/2014/10/21/hostile-subdomain-takeover-using-herokugithubdesk-more/.
+You can read up more about subdomain takeovers here: 
+
+- https://labs.detectify.com/2014/10/21/hostile-subdomain-takeover-using-herokugithubdesk-more/
+- https://www.hackerone.com/blog/Guide-Subdomain-Takeovers
+- https://0xpatrik.com/subdomain-takeover-ns/
 
 ## Safely Demonstrating  a Subdomain takeover
 Claim the subdomain discreetly and serve a harmless file on a hidden page. Do not serve content on the index page. A good proof of concept could consist of an HTML comment served via a random path: