Remove qtgraphicaleffects sources and add note about its state in Qt 6HEADdev

Add a README.md mentioning the documentation on where the ported
effects can be found, as well as how to check out the Qt5 branch.

Pick-to: 6.2
Fixes: QTBUG-95757
Change-Id: Ib47c7e73f8622c8e287df0f74c6f16a5113b357e
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 28 insertions, 0 deletions

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..a02e3ce
--- /dev/null
+++ b/README.md
@@ -0,0 +1,28 @@
+# QtGraphicalEffects
+
+**The QtGraphicalEffects module has been deprecated and is no longer part of Qt.**
+
+The functionality of the module has been partially incorporated into the Qt5Compat module.
+
+The documentation for those parts can be found at
+[Qt 5 Compatibility APIs: Graphical Effects](https://doc.qt.io/qt-6/qtgraphicaleffects5-index.html)
+
+## Working on Qt 5
+
+To work on patches for the Qt 5 series, check out a local branch of the relevant Qt version, e.g.:
+
+```bash
+$ git checkout 5.15
+Branch '5.15' set up to track remote branch '5.15' from 'origin' by rebasing.
+Switched to a new branch '5.15'
+```
+
+## Going back in time
+
+To inspect the code in the `dev` branch prior to its removal, follow these steps:
+
+```bash
+$ git checkout -b my-dev dev~1
+Switched to a new branch 'my-dev'
+```
+