Remove some elements of the index page

As mentioned in https://github.com/PostgREST/postgrest-docs/issues/249,
the embracing the relational model sectin would better fit in a
page about our REST style.

The shared improvements section no longer seems relevant since
we're already an established open source project.

Release notes are not removed but hidden from the index page.

index.rst

@@ -54,21 +54,11 @@ Leak-proof Abstraction
 
 There is no ORM involved. Creating new views happens in SQL with known performance implications. A database administrator can now create an API from scratch with no custom programming.
 
-Embracing the Relational Model
-------------------------------
-
-In 1970 E. F. Codd criticized the then-dominant hierarchical model of databases in his article A Relational Model of Data for Large Shared Data Banks. Reading the article reveals a striking similarity between hierarchical databases and nested http routes. With PostgREST we attempt to use flexible filtering and embedding rather than nested routes.
-
 One Thing Well
 --------------
 
 PostgREST has a focused scope. It works well with other tools like Nginx. This forces you to cleanly separate the data-centric CRUD operations from other concerns. Use a collection of sharp tools rather than building a big ball of mud.
 
-Shared Improvements
--------------------
-
-As with any open source project, we all gain from features and fixes in the tool. It's more beneficial than improvements locked inextricably within custom code-bases.
-
 Getting Support
 ----------------
 
@@ -95,6 +85,7 @@ Translations
 .. toctree::
    :caption: Release Notes
    :titlesonly:
+   :hidden:
 
    release_notes.rst
 
@@ -107,6 +98,7 @@ Translations
 
 .. toctree::
    :caption: How-to guides
+   :name: how-tos
    :titlesonly:
 
    how-tos/embedding-table-from-another-schema.rst