Draft 4.13.1 release notes

Author: marcphilipp

doc/ReleaseNotes4.13.1.md

@@ -0,0 +1,7 @@
+## Summary of changes in version 4.13.1
+
+# Test Runners
+
+### [Pull request #1669:](https://github.com/junit-team/junit/pull/1669) Make `FrameworkField` constructor public
+
+Prior to this change, custom runners could make `FrameworkMethod` instances, but not `FrameworkField` instances. This small change allows for both now, because `FrameworkField`'s constructor has been promoted from package-private to public.

src/site/xdoc/index.xml

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             <li><a href="https://github.com/junit-team/junit4/wiki/Getting-started">Getting started</a></li>
             <li>Release Notes
               <ul>
+<li><a href="https://github.com/junit-team/junit4/blob/HEAD/doc/ReleaseNotes4.13.1.md">4.13.1</a></li>
 <li><a href="https://github.com/junit-team/junit4/blob/HEAD/doc/ReleaseNotes4.13.md">4.13</a></li>
 <li><a href="https://github.com/junit-team/junit4/blob/HEAD/doc/ReleaseNotes4.12.md">4.12</a></li>
 <li><a href="https://github.com/junit-team/junit4/blob/HEAD/doc/ReleaseNotes4.11.md">4.11</a></li>