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.

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

docs/source/contributing.md

@@ -0,0 +1,9 @@
+# Contributing to parsedmarc
+
+
+## Bug reports
+
+Please report bugs on the GitHub issue tracker
+
+<https://github.com/domainaware/parsedmarc/issues>
+