Split and Organise documentation files (#404)

* Set global TOC collapse to false

* Split documentation

I tried to split the index.md file into logical parts, not changing the contents.
I did add a space and change one HTTP URL to HTTPS.

---------

Co-authored-by: Sean Whalen <44679+seanthegeek@users.noreply.github.com>

docs/source/splunk.md

@@ -0,0 +1,22 @@
+### Splunk
+
+Starting in version 4.3.0 `parsedmarc` supports sending aggregate and/or
+forensic DMARC data to a Splunk [HTTP Event collector (HEC)].
+
+The project repository contains [XML files] for premade Splunk
+dashboards for aggregate and forensic DMARC reports.
+
+Copy and paste the contents of each file into a separate Splunk
+dashboard XML editor.
+
+:::{warning}
+Change all occurrences of `index="email"` in the XML to
+match your own index name.
+:::
+
+The Splunk dashboards display the same content and layout as the
+Kibana dashboards, although the Kibana dashboards have slightly
+easier and more flexible filtering options.
+
+[xml files]: https://github.com/domainaware/parsedmarc/tree/master/splunk
+[http event collector (hec)]: http://docs.splunk.com/Documentation/Splunk/latest/Data/AboutHEC