Add explanatory comment for conditional error check

Author: jonathanmendez

toolkit/xre/nsAppRunner.cpp

@@ -4251,6 +4251,8 @@ int XREMain::XRE_mainInit(bool* aExitFlag) {
 #if defined(MOZ_ENTERPRISE)
   rv = XRE_ParseEnterpriseServerURL(*mAppData);
 #  if defined(MOZILLA_OFFICIAL)
+  // Enterprise deployments must have a distribution.ini, but we need to
+  // tolerate local builds
   if (NS_FAILED(rv)) {
     Output(true, "Couldn't read console url from distribution.ini");
     return 1;