Add a note about migrating to the VexFlow organization.

Author: ronyeh

VEXFLOW.md

@@ -0,0 +1,16 @@
+This repository contains VexFlow version 4.2.
+
+VexFlow 4.x will be maintained with bug fixes, but active development has moved to the VexFlow organization at https://github.com/vexflow/vexflow/.
+
+VexFlow was created in 2010 by [Mohit Muthanna Cheppudira](https://github.com/0xfe), and has been worked on by [many contributors](https://github.com/0xfe/vexflow/graphs/contributors).
+
+From 2021-2022, [Rodrigo Vilar](https://github.com/rvilarl) and [Ron Yeh](https://github.com/ronyeh) converted VexFlow to TypeScript, added support for ES modules, and improved the build and deployment process.
+
+In 2023, VexFlow became an organization. The code was permanently forked from [this commit](https://github.com/0xfe/vexflow/commit/b16796b2138d1d8304f1aca6f0401f6c3e34c902):
+
+```
+commit b16796b2138d1d8304f1aca6f0401f6c3e34c902
+Date:   Mon Jul 3 12:58:17 2023 -0700
+```
+
+See https://github.com/vexflow/vexflow/ for the current version of VexFlow.