Add security advisories page

Edward Thomson · Edward Thomson · commit d9a237f3e04e · 2017-01-06T05:59:04.000-06:00
diff --git a/security/index.md b/security/index.md
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+---
+layout: default
+---
+
+# Security Information
+
+Information about security advisories affecting libgit2 and the releases that
+provide resolution.
+
+* **[libgit2 v0.22.1](https://github.com/libgit2/libgit2/releases/tag/v0.22.1)**, January 16, 2015  
+Provides additional protections on symbolic links on case-insensitive
+filesystems, particularly Mac OS X HFS+.
+[Further reading](http://www.edwardthomson.com/blog/another-libgit2-security-update.html).
+
+* **[libgit2 v0.21.3](https://github.com/libgit2/libgit2/releases/tag/v0.21.3)**, December 18, 2015  
+Updates protections on the git repository on case-insensitive filesystems,
+including Windows NTFS and Mac OS X HFS+: CVE 2014-9390.
+[Further reading](https://git-blame.blogspot.co.uk/2014/12/git-1856-195-205-214-and-221-and.html).
