Add security and funding (#794)

Author: shadowspawn

.github/FUNDING.yml

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+github: [tj, shadowspawn]
+tidelift: npm/n

SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+The latest two major versions get security updates.
+
+Pull Requests for security issues will be considered for older versions.
+
+## Reporting a Vulnerability
+
+To report a security vulnerability, please use the
+[Tidelift security contact](https://tidelift.com/security).
+Tidelift will coordinate the fix and disclosure.