Add explaining doc

doc/IMPORT-ISSUES.md

@@ -0,0 +1,11 @@
+## How to import common-js dependency using ES6 syntax
+---
+Until [#6632](https://github.com/vitejs/vite/issues/6632) is fixed, such imports should be done as follows:
+
+```ts
+import * as pkg from "off-color";
+// @ts-ignore 
+const offColor = pkg.offColor ?? pkg.default.offColor;
+```
+
+This way build, dev server and unit tests should all work.