Update security policy

[jbma]

Describe the solution you'd like
We've moved our security reporting to Patchstack, thus we need to update our readme + security reporting :

In the Readme :

== Frequently Asked Questions ==  

= Where do I report security bugs found in this plugin? =  
  
You can report any security bugs found in the source code of the site-reviews plugin through the [Patchstack Vulnerability Disclosure Program](https://patchstack.com/database/vdp/rocket-lazy-load). The Patchstack team will assist you with verification, CVE assignment and take care of notifying the developers of this plugin.
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In the Security.md (file need to be created in Github)

# Security Policy  
  
## Reporting Security Bugs  
  
Please report security bugs found in the site-reviews plugin's source code through the [Patchstack Vulnerability Disclosure Program](https://patchstack.com/database/vdp/rocket-lazy-load). The Patchstack team will assist you with verification, CVE assignment and take care of notifying the developers of this plugin.
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