add texture compression explication

panda/src/doc/eggSyntax.txt

@@ -154,10 +154,10 @@ appear before they are referenced.
     This defines the load format of the image file.  The
     format-definition is one of:
 
-    RGBA, RGBM, RGBA12, RGBA8, RGBA4,
-    RGB, RGB12, RGB8, RGB5, RGB332,
-    LUMINANCE_ALPHA,
-    RED, GREEN, BLUE, ALPHA, LUMINANCE
+      RGBA, RGBM, RGBA12, RGBA8, RGBA4,
+      RGB, RGB12, RGB8, RGB5, RGB332,
+      LUMINANCE_ALPHA,
+      RED, GREEN, BLUE, ALPHA, LUMINANCE
 
     The formats whose names end in digits specifically request a
     particular texel width.  RGB12 and RGBA12 specify 48-bit texels
@@ -178,6 +178,25 @@ appear before they are referenced.
     specified; if it does not, the egg loader will attempt to provide
     the closest match that does.
 
+  <Scalar> compression { compression-mode }
+
+    Defines an explicit control over the real-time compression mode
+    applied to the texture.  The various options are:
+
+      DEFAULT OFF ON
+      FXT1 DXT1 DXT2 DXT3 DXT4 DXT5
+
+    This controls the compression of the texture when it is loaded
+    into graphics memory, and has nothing to do with on-disk
+    compression such as JPEG.  If this option is omitted or "DEFAULT",
+    then the texture compression is controlled by the
+    compressed-textures config variable.  If it is "OFF", texture
+    compression is explicitly off for this texture regardless of the
+    setting of the config variable; if it is "ON", texture compression
+    is explicitly on, and a default compression algorithm supported by
+    the driver is selected.  If any of the other options, it names the
+    specific compression algorithm to be used.
+
   <Scalar> wrap { repeat-definition }
   <Scalar> wrapu { repeat-definition }
   <Scalar> wrapv { repeat-definition }