Write the basic guide and add the needed images

docs/guides/stonesense-art-guide.rst

@@ -2,3 +2,56 @@
 
 Stonesense art creation guide
 =============================
+
+Understanding Sprites
+---------------------
+Understanding how Stonesense deals with sprites is central to anyone who wishes to modify the content.
+The scheme is not very complicated, and this guide will give a short introduction to how they work.
+The way sprites are loaded is fairly generalized. With the exception of floors, which we will discuss later,
+all sprites are 32x32 pixels big and come in groups known as Sprite Sheets. All sprites are loaded and
+rendered in 32-bit full-color PNGs.
+
+Here's an example of a typical Stonesense sprite: 
+.. figure:: ../images/Stonesene_sprite_sample.png
+   :align: left
+
+Note that, in order not to conflict with neighboring sprites, a sprite must actually be within a smaller
+area than its 32x32 block. A template for the area used by most sprites is:
+.. figure:: ../images/Stonesene_sprite_template.png
+   :align: left
+
+The solid area is the floor space taken up by a sprite, while the dotted box indicates the volume above this
+area corresponding to one z-level. 
+
+Sprite Sheets
+-------------
+There can be an arbitrary number of sprite sheets configured for Stonesense, yet some are always present as
+they contain default sprites (see further down). Most of the content XML files allow users to specify sprite
+sheets, and this is done by adding a file attribute to the content nodes. By convention sprite sheets should
+be placed in their appropriate folder, with creature sprite sheets in the creatures folder etc.
+
+Sprite Index
+------------
+Sprite Index (sometimes referred to as Sheet Index) is a concept for referring to a specific sprite on a sheet.
+The index starts with the upper left sprite which has index zero. It then increments to the right. Stonesense
+is hardcoded to 20 sprites wide sheets, this means that the last sprite to the right in the first row has Sprite
+Index 19. The first sprite on the second row has index 20. This boundary is hardcoded and changing the size of
+the sheet will not affect it.
+
+This image shows how sprites are indexed. Note: Grid added for readability.
+.. figure:: ../images/Stonesense_indexed_sprites.png
+   :align: left
+
+Specific Sprite Sheets
+----------------------
+**objects.png** is the default sheet for buildings and vegetation. Also used for all hard-coded content, like default
+plants, the cursor, default walls and liquid.
+
+**creatures.png** is the default sprite sheet for creatures. If no file is specified in a creature node, this is the
+sheet it will use.
+
+**floors.png** holds all the Stonesense floors. Unlike the other sprite sheet, this sheet is hard-coded with sprite
+dimensions of 32x20 pixels.
+
+Stonesense is fully configurable in the way it renders creatures. No information is hardcoded, but rather loaded
+from the creature databases found in the creatures directory.