add examples about section

docs/examples_about.md

@@ -0,0 +1,6 @@
+The examples in this section are configured as working Juptyer Notebooks. They
+can be downloaded directly by using the :material-download:{ .lg } icon at the top of the
+page of each example.
+
+The data used for these examples is available from the Github repository 
+[examples/data](https://github.com/trhallam/segysak/tree/main/examples/data) directory.