Problem: Code Reference docs hidden in appendices (#2473)

Solution: Move the Code Reference docs into their own section

docs/server/source/code-reference/index.rst

@@ -0,0 +1,24 @@
+
+.. Copyright BigchainDB GmbH and BigchainDB contributors
+   SPDX-License-Identifier: (Apache-2.0 AND CC-BY-4.0)
+   Code is Apache-2.0 and docs are CC-BY-4.0
+
+Code Reference
+==============
+
+This section contains auto-generated documentation of various functions, classes and methods
+in the BigchainDB Server code, based on Python docstrings in the code itself.
+
+.. warning::
+
+   While we try to keep docstrings accurate,
+   if you want to know *for sure* what the code does,
+   then you have to read the code itself.
+
+.. toctree::
+   :maxdepth: 1
+
+   the-bigchaindb-class
+   backend
+   commands
+