Add security and maintenance files (#324)

* Add security and maintenance files

* Fix image heights

MAINTENANCE.md

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+## Maintenance Policy
+
+<a href='https://hellostealth.org'><img src='logo.svg' height='120' alt='Xip Logo' aria-label='hellostealth.org' /></a>
+
+## Versioning
+
+Stealth follows [semantic versioning](https://semver.org).
+
+```
+MAJOR.MINOR.PATCH
+```
+
+While we intend to do our best to ensure that even MAJOR version changes do not introduce breaking changes, we can't guarantee it yet at this point in the project.
+
+Rest assured, though, that all feature deprecations will be either "gently" removed or just permanently deprecated.
+
+
+## Currently Maintained Versions
+
+* :white_check_mark: - These versions will receive feature updates, bugfixes, and security updates.
+* :heavy_check_mark: - These versions will only receive bugfixes and security updates.
+* :x: - These versions are no longer maintained. Please upgrade.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 2.x     | :white_check_mark: |
+| 1.1.x   | :heavy_check_mark: |
+| < 1.1   | :x:                |

SECURITY.md

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+## Security Policy
+
+<a href='https://hiremav.com/security'><img src='logo.svg' height='120' alt='Stealth Logo' aria-label='Stealth security' /></a>
+
+## Reporting a Vulnerability
+
+**Do not open up a GitHub issue if the bug is a security vulnerability in Stealth**.
+
+Instead, please refer to Mav's [security policy](https://hiremav.com/security).
+
+## Supported Versions
+
+Please see our [maintenance policy](https://github.com/hellostealth/stealth/blob/master/MAINTENANCE.md) for currently supported versions.