Update documentation to clarify the effects of using shadows without shaders.

docs/source/reference/modding/settings/shaders.rst

@@ -1,6 +1,7 @@
 Shader Settings
 ###############
 
+.. _force-shaders-label:
 force shaders
 -------------
 

docs/source/reference/modding/settings/shadows.rst

@@ -13,6 +13,10 @@ enable shadows
 
 Enable or disable the rendering of shadows.
 Unlike in the original Morrowind engine, 'Shadow Mapping' is used, which can have a performance impact, but has more realistic results.
+When used in fixed-function mode, shadowed regions will appear completely black.
+To prevent this, enable :ref:`force-shaders-label`.
+A keen developer may be able to implement something better using the advice of `this post<https://github.com/OpenMW/openmw/pull/1547#issuecomment-369657381>`_, but it may be more difficult than it seems.
+
 
 number of shadow maps
 ---------------------

files/settings-default.cfg

@@ -474,7 +474,7 @@ companion w = 0.38
 companion h = 0.63
 
 [Shadows]
-# Enable or disable shadows.
+# Enable or disable shadows. Bear in mind that when used without "[Shaders]/force shaders" set to true (i.e. objects and terrain are rendered in fixed-function mode) shadowed areas will be completely black. As such, it is recommended to use this feature in conjunction with shaders.
 enable shadows = false
 # How many shadow maps to use - more of these means each shadow map texel covers less area, producing better looking shadows, but may decrease performance.
 number of shadow maps = 1