Pose Library: explain why the 'for keymap' operators are there

The for-keymap version of the apply/blend operators take the Window
Manager's `poselib_flipped` property, and passes it to the regular
apply/blend operator. This makes it possible to bind a key to the
operator and still have it respect the global "Flip Pose" checkbox.

This behaviour was already in, this commit just adds a comment that
explains this.

No functional changes.

pose_library/operators.py

@@ -399,6 +399,10 @@ class POSELIB_OT_pose_asset_select_bones(PoseAssetUser, Operator):
         return cls.bl_description.replace("Select", "Deselect")
 
 
+# This operator takes the Window Manager's `poselib_flipped` property, and
+# passes it to the `POSELIB_OT_blend_pose_asset` operator. This makes it
+# possible to bind a key to the operator and still have it respect the global
+# "Flip Pose" checkbox.
 class POSELIB_OT_blend_pose_asset_for_keymap(Operator):
     bl_idname = "poselib.blend_pose_asset_for_keymap"
     bl_options = {"REGISTER", "UNDO"}
@@ -421,6 +425,10 @@ class POSELIB_OT_blend_pose_asset_for_keymap(Operator):
         return bpy.ops.poselib.blend_pose_asset(context.copy(), 'INVOKE_DEFAULT', flipped=flipped)
 
 
+# This operator takes the Window Manager's `poselib_flipped` property, and
+# passes it to the `POSELIB_OT_apply_pose_asset` operator. This makes it
+# possible to bind a key to the operator and still have it respect the global
+# "Flip Pose" checkbox.
 class POSELIB_OT_apply_pose_asset_for_keymap(Operator):
     bl_idname = "poselib.apply_pose_asset_for_keymap"
     bl_options = {"REGISTER", "UNDO"}