Add comments warning against the use of dx_build_app.main().
Add comments warning against the use of dx_build_app.main().

olegnev/dx-toolkit,dnanexus/dx-toolkit,dnanexus/dx-toolkit,olegnev/dx-toolkit,olegnev/dx-toolkit,andyshinn/dx-toolkit,olegnev/dx-toolkit,andyshinn/dx-toolkit,andyshinn/dx-toolkit,dnanexus/dx-toolkit,andyshinn/dx-toolkit,dnanexus/dx-toolkit,dnanexus/dx-toolkit,andyshinn/dx-toolkit,andyshinn/dx-toolkit,johnwallace123/dx-toolkit,dnanexus/dx-toolkit,jhuttner/dx-toolkit,olegnev/dx-toolkit,jhuttner/dx-toolkit,jhuttner/dx-toolkit,jhuttner/dx-toolkit,johnwallace123/dx-toolkit,johnwallace123/dx-toolkit,dnanexus/dx-toolkit,andyshinn/dx-toolkit,johnwallace123/dx-toolkit,johnwallace123/dx-toolkit,jhuttner/dx-toolkit,johnwallace123/dx-toolkit,jhuttner/dx-toolkit,dnanexus/dx-toolkit,johnwallace123/dx-toolkit,jhuttner/dx-toolkit,johnwallace123/dx-toolkit,olegnev/dx-toolkit,andyshinn/dx-toolkit,olegnev/dx-toolkit,jhuttner/dx-toolkit,olegnev/dx-toolkit