Remove stale reference to PySide2

README.md

@@ -84,9 +84,9 @@ Limitations
  supported, for example text on path, line wrapping or style changes mid
  text element.
 * **Depends on [Qt for Python (a.k.a.
- PySide2)](https://wiki.qt.io/Qt_for_Python).** This is a relatively
+ PySide6)](https://wiki.qt.io/Qt_for_Python).** This is a relatively
  non-trivial dependency but is easy to install from
- [PyPI](https://pypi.org/project/PySide2/) on most platforms. Unfortunately it
+ [PyPI](https://pypi.org/project/PySide6/) on most platforms. Unfortunately it
  makes svgoutline subject to the same bugs (e.g.
  [QTBUG-72997](https://bugreports.qt.io/browse/QTBUG-72997) which at the time
  of writing causes text outlines and dash patterns to render too small).