Add alternate text on images

It makes images (a bit) more accessible.

content/pages/0.index.rst

@@ -37,7 +37,7 @@ highlighting.
 * Source: https://github.com/dbcli/pgcli
 
 .. image:: {filename}/images/image01.png
-   :alt: Screenshot
+   :alt: Screenshot of pgcli showing SQL output and auto-completion on table names
    :width: 750px
 
 Quick Start

content/pages/completion.md

@@ -14,28 +14,43 @@ Here are a few examples of smart completion.
 
 Only table names from the current database are suggested after the FROM keyword.
 
-<img src="images/docs/table.png" width=750 align="center">
+.. image:: images/docs/table.png
+   :alt: Screenshot of pgcli auto-completion on table names in `select * from ‸`
+   :width: 750px
+   :align: center
 
 ### Column
 
 Column names from the current table are suggested after the WHERE clause.
 
-<img src="images/docs/column.png" width=750 align="center">
+.. image:: images/docs/column.png
+   :alt: Screenshot of pgcli auto-completion on column names in `select * from django_site where ‸`
+   :width: 750px
+   :align: center
 
-### Insert 
+### Insert
 
 Insert statement will suggest the column names.
 
-<img src="images/docs/insert.png" width=750 align="center">
+.. image:: images/docs/insert.png
+   :alt: Screenshot of pgcli auto-completion in `insert into django_site values (‸`
+   :width: 750px
+   :align: center
 
 ### Alias
 
 Aliases in the query are resolved and the columns from the table aliases are suggested.
 
-<img src="images/docs/alias.png" width=750 align="center">
+.. image:: images/docs/alias.png
+   :alt: Screenshot of pgcli auto-completion on aliases tables in `select * from django_site d join auth_group a on d.‸`
+   :width: 750px
+   :align: center
 
 ## Fuzzy Match
 
 The completions are matched using a [fuzzy algorithm](http://blog.amjith.com/fuzzyfinder-in-10-lines-of-python). For example typing 'djmi' will match the table 'django_migrations' because 'djmi' has parts of matching substrings. Here's an example:
 
-<img src="images/docs/fuzzy.png" width=750 align="center">
+.. image:: images/docs/fuzzy.png
+   :alt: Screenshot of pgcli auto-completion with fuzzy matching in `select * from aup‸` that proposes 'auth_permission', 'auth_group', etc.
+   :width: 750px
+   :align: center