docs: Replace the block description list with references.

Match the listing in the Block Description subsection with the listing
in the original source, and use references to the sections instead of
using an auto generated table of contents.

Signed-off-by: Amr Gouhar <aagouhar@efabless.com>
Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>
diff --git a/docs/user_guide.rst b/docs/user_guide.rst
index 5701072..917fa9b 100644
--- a/docs/user_guide.rst
+++ b/docs/user_guide.rst
@@ -208,11 +208,6 @@
 Block Architecture Overview
 ---------------------------
 
-The following sections describe each of the blocks in detail:
-
-.. contents:: :local:
-   :depth: 1
-
 Block Description
 ~~~~~~~~~~~~~~~~~
 .. todo:: :cell:`sky130_fd_io__gpio` is not yet publicly available.
@@ -226,9 +221,24 @@
 and a special I/O (:cell:`sky130_fd_io__sio`), a reference generator (:cell:`sky130_fd_io__refgen`) for providing voltage references to the :cell:`sky130_fd_io__sio` and Power and Ground (PG)
 cells that make up the I/O ring.
 
+The following sections describe each of the blocks in detail:
+
 A single table comparison of all features across different IO's is provided in :numref:`io features comparison`.
 
-.. io-common-features_
+
+*  I/O [1]_ Common Features, section :ref:`io-common-features`.
+*  :cell:`sky130_fd_io__gpio`, :cell:`sky130_fd_io__gpiosf` Additional Features, section :ref:`sky130_fd_io__gpio-additional-features`.
+*  :cell:`sky130_fd_io__gpiov2` Additional Features, section :ref:`sky130_fd_io__gpiov2-additional-features`.
+*  :cell:`sky130_fd_io__gpio_ovtv2` Additional Features, section :ref:`sky130_fd_io__gpio_ovtv2-additional-features`.
+*  :cell:`sky130_fd_io__sio` Additional Features, :ref:`sky130_fd_io__sio-additional-features`.
+*  :cell:`sky130_fd_io__refgen` Features, :ref:`sky130_fd_io__refgen-features`.
+*  PG pads (ESD), :ref:`pg-pads`.
+*  Overlay Cells, :ref:`overlay-cells`.
+*  Power Detectors, :ref:`power-detector`.
+
+
+
+.. _io-common-features:
 
 I/O\ [1]_ Common Features
 ~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -480,6 +490,7 @@
    - Latched means that the input and output enable are latched. This is the same functionality as mentioned in :numref:`io vil vih`.
    - Normal refers any mode other than Sleep modes
 
+.. _sky130_fd_io__gpio-additional-features:
 :cell:`sky130_fd_io__gpio` Additional Features
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 .. todo:: :cell:`sky130_fd_io__gpio` is not yet publicly available.
@@ -632,6 +643,7 @@
 ``tie_hi_esd``).
 All other :cell:`sky130_fd_io__gpio` cells have their input buffers disabled while XRES is asserted (``enable_inp_h`` is ``tie_lo_esd``).
 
+.. _sky130_fd_io__gpiov2-additional-features:
 :cell:`sky130_fd_io__gpiov2` Additional Features
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -748,7 +760,7 @@
    |         |          |      |                   |                   |                     | * WPD Mode                |
    +---------+----------+------+-------------------+-------------------+---------------------+---------------------------+
 
-
+.. _sky130_fd_io__gpio_ovtv2-additional-features:
 :cell:`sky130_fd_io__gpio_ovtv2` Additional Features
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -864,6 +876,7 @@
    |       |          |      |              |                   |                                           | * WPD Mode    |
    +-------+----------+------+--------------+-------------------+-------------------------------------------+---------------+
 
+.. _sky130_fd_io__sio-additional-features:
 :cell:`sky130_fd_io__sio` Additional Features
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -975,6 +988,7 @@
 Notice that the input buffer and output buffer configurations can be selected independently.
 For example, the standard single-ended input buffer and the regulated output buffer can be selected.
 
+.. _sky130_fd_io__refgen-features:
 :cell:`sky130_fd_io__refgen` (Reference Generator) Features
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -1230,6 +1244,7 @@
 two amuxbus's.
 When connecting ``amux_a_l`` and ``amux_a_r`` care must be taken to disconnect the mid-node and then close the right and left switch.
 
+.. _pg-pads:
 PG pads (ESD)
 ~~~~~~~~~~~~~
 .. todo:: :cell:`sky130_fd_io__top_hvclamp_wopad`,
@@ -1494,6 +1509,7 @@
    | Hi-Z | Hi-Z        |
    +------+-------------+
 
+.. _overlay-cells:
 Overlay Cells
 ~~~~~~~~~~~~~
 
@@ -1558,7 +1574,8 @@
    | 11   | :cell:`sky130_fd_io__overlay_vssd_hvc`  | :cell:`sky130_fd_io__top_ground_hvc_wpad` | VSSD  power pad | HV ESD clamp     |
    +------+-----------------------------------------+-------------------------------------------+-----------------+------------------+
 
-Power detector
+.. _power-detector:
+Power Detector
 ~~~~~~~~~~~~~~
 .. todo:: :cell:`sky130_fd_io__top_pwrdet` is not yet publicly available.