Added short usage instructions
Added short usage instructions as per comment: https://github.com/bokeh/bokeh/pull/8011#issuecomment-399509585)
Create a simple dashboard based on Bootstrap templates.
+This is a bokeh directory application. To run it, enter the following command at a Bash or Windows command prompt:
+
+```{bash}
+bokeh serve --show dash
+```
+
+See also the [users guide on bokeh directory applications](https://bokeh.pydata.org/en/latest/docs/user_guide/server.html#directory-format), for more detail.
+
# Licences
This example uses vendored code from the following projects:
