Various additions and updates to the main list (#76)

* Update Readme.md

Added two relevant tools. Copied the description of each one from its Readme.

* Update Readme.md

Roll back addition of Whisparr due to adult content.

* Update Readme.md

Remove existing reference to Bonarr due to adult content.

* Update Readme.md

Add a few dashboard tools:

* Homepage and Homarr seem very popular and highly regarded
* starbase-80 is a smaller project run by one guy

* Update Readme.md

Updates to Audiobooks section:
* Added two new servers (AudioBookShelf and Kavita).
* Grouped the links by type
* Added missing descriptions

* Update Readme.md

Add two voice chat servers

* Update Readme.md

Add a new P2P tool, and a new section for a tool to host your own dropbox-like server.

* Update Readme.md

Added link in Contents to new section added in 43c122527b

* Update Readme.md

Added one more file sharing tool

* Update Readme.md

Added an authentication manager/identity provider (new section)

* Update Readme.md

Updates to Seedbox Hosting Providers section:

Online.net is now owned by Scaleway and called Scaleway Dedibox; so replaced the Online.net listing accordingly.

Removed the star from this item, since I don't know if it is recommended.

Added a star to seedboxes.cc, which I have been using for years and works extremely well. Extended its description.

* Update Contributing.md

Added a note stating that adult content is not allowed.

Contributing.md

@@ -11,6 +11,7 @@ Ensure your pull request adheres to the following guidelines:
 - Include a description of the link you're adding if possible
 - If you're changing section headers, ensure you update the contents at the top too
 - If you're adding a new section, ensure you give it a unique name
+- No links to tools or sites focused on adult content/porn
 
 Thank you for your suggestions!