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, 0 insertions, 1 deletions

diff --git a/.tag b/.tag
deleted file mode 100644
index 6828f88..0000000
--- a/.tag
+++ /dev/null
@@ -1 +0,0 @@
-$Format:%H$