Add security advisory notice for CVE-2020-27955.

Author: bk2204

_includes/home/secondary.html

@@ -2,14 +2,10 @@
   <div class="wrapper">
 
     <div class="column">
-      <a class="dot-com-announcement js-os-data" data-os-attr="href" data-ga-params="download,banner"
-         href="https://github.com/git-lfs/git-lfs/releases/latest"
-         data-os-mac="https://github.com/git-lfs/git-lfs/releases/download/v{{site.git-lfs-release}}/git-lfs-darwin-amd64-v{{site.git-lfs-release}}.zip"
-         data-os-windows="https://github.com/git-lfs/git-lfs/releases/download/v{{site.git-lfs-release}}/git-lfs-windows-v{{site.git-lfs-release}}.exe"
-         data-os-linux="https://github.com/git-lfs/git-lfs/releases/download/v{{site.git-lfs-release}}/git-lfs-linux-amd64-v{{site.git-lfs-release}}.tar.gz">
-         GitHub.com support now available. <br/><span>Install the client to get started</span>.</a>
+      <a class="dot-com-announcement" data-ga-params="banner"
+         href="https://github.com/git-lfs/git-lfs/security/advisories/GHSA-4g4p-42wc-9f3m">
+        Git LFS security update:<br/><span>Windows users should update to 2.12.1 or newer</span>.</a>
       </a>
-
     </div>