misc: update GH issue templates

- Use config.yml to prevent creating issues with a blank template
- Don't use a template to direct people to the forum
- Create a security policy template

.github/ISSUE_TEMPLATE/2-help.md

----
-name: Need help with Jitsi Meet?
-about: Please ask it in our community at https://community.jitsi.org
-
----
-
-If you have a question about Jitsi Meet that is not a bug report or feature
-request, please post it in https://community.jitsi.org
-
-Questions posted to this repository will be closed.

.github/ISSUE_TEMPLATE/config.yml

+blank_issues_enabled: false
+contact_links:
+  - name: Need help with Jitsi Meet?
+    url: https://community.jitsi.org
+    about: Please ask it in our community.

README.md

 
 ## Security issues
 
-We take security very seriously and develop all Jitsi projects to be secure and safe.
-
-If you find (or simply suspect) a security issue in any of the Jitsi projects, please send us an email to security@jitsi.org.
-
-**We encourage responsible disclosure for the sake of our users, so please reach out before posting in a public space.**
+For information on reporting security vulnerabilities in Jitsi Meet, see [SECURITY.md](./SECURITY.md).
 
 ## Acknowledgements
 

.github/ISSUE_TEMPLATE/4-security-issues.md → SECURITY.md

----
-name: Security issues
-about: Please email security@jitsi.org
+# Security
 
----
+## Reporting security issuess
 
 We take security very seriously and develop all Jitsi projects to be secure and safe.
 
 If you find (or simply suspect) a security issue in any of the Jitsi projects, please send us an email to security@jitsi.org.
 
-We encourage responsible disclosure for the sake of our users, so please reach out before posting in a public space.
+**We encourage responsible disclosure for the sake of our users, so please reach out before posting in a public space.**