add SECURITY.md

Author: cowtowncoder

SECURITY.md

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+# Security Policy
+
+Last Updated: 2021-09-30
+
+## Supported Versions
+
+Current status of open branches, with new releases, can be found from [Jackson Releases](https://github.com/FasterXML/jackson/wiki/Jackson-Releases)
+wiki page
+
+## Reporting a Vulnerability
+
+The recommended mechanism for reporting possible security vulnerabilities follows
+so-called "Coordinated Disclosure Plan" (see [definition of DCP](https://vuls.cert.org/confluence/display/Wiki/Coordinated+Vulnerability+Disclosure+Guidance)
+for general idea). The first step is to file a [Tidelift security contact](https://tidelift.com/security):
+Tidelift will route all reports via their system to maintainers of relevant package(s), and start the
+process that will evaluate concern and issue possible fixes, send update notices and so on.
+Note that you do not need to be a Tidelift subscriber to file a security contact.
+
+Alternatively you may also report possible vulnerabilities to `info` at fasterxml dot com
+mailing address. Note that filing an issue to go with report is fine, but if you do that please
+DO NOT include details of security problem in the issue but only in email contact.
+This is important to give us time to provide a patch, if necessary, for the problem.