Add a comment for Windows text editor in the Streamdevice tutorial

[lcaouen]

Windows Text Editors don't add automatically a new line at the end of the file.
Please add a comment to the streamdevice tutorial : do not forget to add a new empty line at the files.
For instance, if the line is missing at the end of st.cmd then the ioc does not start because it does not take into account the iocInit() instruction

https://github.com/epics-extensions/EPNix/blob/master/docs/ioc/tutorials/streamdevice.rst

[minijackson]

Note: in addition to mentioning the final newline issue in the StreamDevice tutorial, I think it'd be good to ship an .editorconfig file in the EPNix template, so that VSCode and other editors automatically add this newline.