Document conformance break of vertex attrib 0

Change-Id: I6528f3e3796ca0381de95d6b020a161ac996fa73
Task-number: QTBUG-45175
Reviewed-by: Pasi Keränen <pasi.keranen@digia.com>

src/imports/qtcanvas3d/doc/src/qtcanvas3d-index.qdoc

@@ -66,5 +66,6 @@
         \li \l{Qt Canvas 3D QML Types}
         \li \l{Qt Canvas 3D Examples}
         \li \l{Qt Canvas 3D Logging}
+        \li \l{Qt Canvas 3D Known WebGL Conformance Issues}
     \endlist
 */

src/imports/qtcanvas3d/doc/src/qtcanvas3d.qdoc

@@ -182,3 +182,17 @@
              to find root causes of rendering errors.
     \endtable
 */
+
+/*!
+ * \page qtcanvas3d-conformance-issues-html
+ * \title Qt Canvas 3D Known WebGL Conformance Issues
+ *
+ * \brief Known WebGL conformance issues
+ *
+ * \list
+ *      \li No emulation for vertex attrib 0 arrays. Always have vertex attrib 0 array enabled.
+ *      In desktop OpenGL on some platforms (for example OS X), nothing gets drawn if vertex attrib
+ *      0 is not array-enabled. You can use bindAttribLocation() to force a vertex attribute to use
+ *      location 0, and use enableVertexAttribArray() to make it array-enabled.
+ * \endlist
+ */