include: glx_extint.h add comment for xorgGlxCreateVendor

Add warning, that xorgGlxCreateVendor need to be called once

Signed-off-by: Tautvis <gtautvis@gmail.com>

include/glx_extinit.h

@@ -42,6 +42,11 @@ struct __GLXprovider {
 extern __GLXprovider __glXDRISWRastProvider;
 
 void GlxPushProvider(__GLXprovider * provider);
+
+/**
+ * @brief xorgGlxCreateVendor adds default glx vendor callback
+ * @warning this function need to be called once, because it installs `catch-all` style which always succeed
+ */
 void xorgGlxCreateVendor(void);
 
 #else /* GLXEXT */