Added missing file for previous commit.

Author: Stewori

legacy-dev.md

@@ -0,0 +1,11 @@
+---
+title: Legacy
+---
+## Development before move to Github
+
+### [Bug tracker](https://bugs.jython.org/)
+
+### [Mercurial](https://hg.python.org/jython/)
+
+### [Github mirror](https://github.com/jython/frozen-mirror/)
+This mirror is now frozen.