Add documentation of spacecraftinstrument module types (closes #1847)

modules/spacecraftinstruments/rendering/renderablefov.cpp

@@ -142,7 +142,11 @@ namespace {
         }
     }
 
-    // Needs support for std::map first for the frameConversions
+    // This Renderable type shows a visual representation of a spacecraft instrument's
+    // field-of-view. Information about the field-of-view are extracted from SPICE kernels
+    // that must be loaded with the correct information. By default a field-of-view is
+    // only visible while an instrument is active, but the field-of-view can be made
+    // visible at all times through the `AlwaysDrawFov` setting.
     struct [[codegen::Dictionary(RenderableFov)]] Parameters {
         // The SPICE name of the source body for which the field of view should be
         // rendered.