Add a Feature Matrix to the documentation.

That helps having both an overview of what pgloader is capable of doing with
a database migration, and also documenting that some sources don't have the
full support for some features yet.

Author: dimitri

docs/index.rst

@@ -6,6 +6,18 @@
 Welcome to pgloader's documentation!
 ====================================
 
+pgloader loads data from various sources into PostgreSQL. It can transform
+the data it reads on the fly and submit raw SQL before and after the
+loading. It uses the `COPY` PostgreSQL protocol to stream the data into the
+server, and manages errors by filling a pair of *reject.dat* and
+*reject.log* files.
+
+Thanks to being able to load data directly from a database source, pgloader
+also supports from migrations from other productions to PostgreSQL. In this
+mode of operations, pgloader handles both the schema and data parts of the
+migration, in a single unmanned command, allowing to implement **Continuous
+Migration**.
+
 .. toctree::
    :maxdepth: 2
    :caption: Table Of Contents:

docs/intro.rst

@@ -53,6 +53,47 @@ PostgreSQL <http://mysqltopgsql.com/project/>`_ webpage.
 In order to be able to follow this great methodology, you need tooling to
 implement the third step in a fully automated way. That's pgloader.
 
+Features Matrix
+---------------
+
+Here's a comparison of the features supported depending on the source
+database engine. Most features that are not supported can be added to
+pgloader, it's just that nobody had the need to do so yet.
+
+==========================   =======  ======  ======  ===========  =========
+Feature                      SQLite   MySQL   MS SQL  PostgreSQL   Redshift 
+==========================   =======  ======  ======  ===========  =========
+One-command migration           ✓       ✓       ✓           ✓          ✓
+Continuous Migration            ✓       ✓       ✓           ✓          ✓
+Schema discovery                ✓       ✓       ✓           ✓          ✓
+Partial Migrations              ✓       ✓       ✓           ✓          ✓
+Schema only                     ✓       ✓       ✓           ✓          ✓
+Data only                       ✓       ✓       ✓           ✓          ✓
+Repeatable (DROP+CREATE)        ✓       ✓       ✓           ✓          ✓
+User defined casting rules      ✓       ✓       ✓           ✓          ✓
+Encoding Overrides              ✗       ✓       ✗            ✗          ✗
+On error stop                   ✓       ✓       ✓           ✓          ✓
+On error resume next            ✓       ✓       ✓           ✓          ✓
+Pre/Post SQL commands           ✓       ✓       ✓           ✓          ✓
+Post-Schema SQL commands        ✗       ✓       ✓           ✓          ✓
+Primary key support             ✓       ✓       ✓           ✓          ✓
+Foreign key support             ✓       ✓       ✓           ✓          ✗
+Incremental data loading        ✓       ✓       ✓           ✓          ✓
+Online ALTER schema             ✓       ✓       ✓           ✓          ✓
+Materialized views              ✗       ✓       ✓           ✓          ✓
+Distribute to Citus             ✗       ✓       ✓           ✓          ✓
+==========================   =======  ======  ======  ===========  =========
+
+For more details about what the features are about, see the specific
+reference pages for your database source.
+
+For some of the features, missing support only means that the feature is not
+needed for the other sources, such as the capability to override MySQL
+encoding metadata about a table or a column. Only MySQL in this list is left
+completely unable to guarantee text encoding. Or Redshift not having foreign
+keys.
+
+
 Commands
 --------