docs: initial port of hugo to sphinx, including rtd theme

docs/index.rst

@@ -3,18 +3,68 @@
    You can adapt this file completely to your liking, but it should at least
    contain the root `toctree` directive.
 
-Welcome to zrepl's documentation!
-=================================
+zrepl - ZFS replication
+-----------------------
+
+.. ATTENTION::
+    zrepl as well as this documentation is still under active development.
+    It is neither feature complete nor is there a stability guarantee on the configuration format.
+    Use & test at your own risk ;)
+
+Getting started
+~~~~~~~~~~~~~~~
+
+The [5 minute tutorial setup]({{< relref "tutorial/_index.md" >}}) gives you a first impression.
+
+Main Features
+~~~~~~~~~~~~~
+
+* Filesystem Replication
+    * [x] Local & Remote
+    * [x] Pull mode
+    * [ ] Push mode
+    * [x] Access control checks when pulling datasets
+    * [x] [Flexible mapping]({{< ref "configuration/map_filter_syntax.md" >}}) rules
+    * [x] Bookmarks support
+    * [ ] Feature-negotiation for
+        * Resumable `send & receive`
+        * Compressed `send & receive`
+        * Raw encrypted `send & receive` (as soon as it is available)
+* Automatic snapshot creation
+    * [x] Ensure fixed time interval between snapshots
+* Automatic snapshot [pruning]({{< ref "configuration/prune.md" >}})
+    * [x] Age-based fading (grandfathering scheme)
+* Flexible, detailed & structured [logging]({{< ref "configuration/logging.md" >}})
+    * [x] `human`, `logfmt` and `json` formatting
+    * [x] stdout, syslog and TCP (+TLS client auth) outlets
+* Maintainable implementation in Go
+    * [x] Cross platform
+    * [x] Type safe & testable code
+
+Contributing
+~~~~~~~~~~~~
+
+We are happy about any help we can get!
+
+* Explore the codebase
+    * These docs live in the `docs/` subdirectory
+* Document any non-obvious / confusing / plain broken behavior you encounter when setting up zrepl for the first time
+* Check the *Issues* and *Projects* sections for things to do
+
+{{% panel header="<i class='fa fa-github'></i> Development Workflow"%}}
+[The <i class='fa fa-github'></i> GitHub repository](https://github.com/zrepl/zrepl) is where all development happens.<br />
+Make sure to read the [Developer Documentation section](https://github.com/zrepl/zrepl) and open new issues or pull requests there.
+{{% /panel %}}
+
+Table of Contents
+~~~~~~~~~~~~~~~~~
 
 .. toctree::
    :maxdepth: 2
    :caption: Contents:
 
-
-
-Indices and tables
-==================
-
-* :ref:`genindex`
-* :ref:`modindex`
-* :ref:`search`
+   tutorial
+   installation
+   configuration
+   implementation
+   pr