add more instructions for setting map

docs/build.md

@@ -23,7 +23,9 @@ AirSim code has two external dependencies: Eigen library and Boost library.
 To run the simulator, you need an environment and its very easy to create one! [Unreal Marketplace](https://www.unrealengine.com/marketplace) has dozens of prebuilt extra-ordinarily detailed [environments](https://www.unrealengine.com/marketplace/content-cat/assets/environments) ranging from Moon to Mars and everything in between. The one we have used for testing is called [Modular Neighborhood Pack](https://www.unrealengine.com/marketplace/modular-neighborhood-pack) but you can use any environment.
   1. Either purchase an environment from Unreal Marketplace or choose one of the free ones such as [Infinity Blade series](https://www.unrealengine.com/marketplace/infinity-blade-plain-lands). Alternatively, if you look under the Learn tab in Epic Game Launcher, you will find many free samples that you can use. One of our favorites is "A Boy and His Kite" which is a 100 square miles of highly detailed environment (caution: you will need *very* beefy PC to run it!).
   ![Epic Launcher - Learn](images/epic_launcher_learn.png)
-  2. Once you have the environment, you can simply go to the Library tab of the Epic Game Launcher and add in to any project you like. We recommend creating a new blank C++ project with no Starter Content and add your environment in to it. Tip: if the environment comes with MatineeActor, delete it to avoid any demo sequences.
+  2. Once you have the environment, you can simply go to the Library tab of the Epic Game Launcher and add in to any project you like. We recommend creating a new blank C++ project with no Starter Content and add your environment in to it.
+  3. If the environment comes with MatineeActor, delete it to avoid any startup demo sequences. There might be other ways to remove it as well, for example, click on Blueprints button, then Level Blueprint and then look at Begin Play event in Event Graph. You might want to disconnect any connections that may be starting "matinee".
+  4. You might have to set default map for your project. For example, if you are using Modular Neighborhood Pack, set the Editor Starter Map as well as Game Default Map to Demo_Map in Project Settings > Maps & Modes..
 
 ## Install the AirSim Plugin
 ### Copy plugins folder
@@ -64,7 +66,7 @@ You are all ready to go now!
 1. Right click on the Unreal project .uproject file, then Generate Visual Studio Project files. 
 2. Double click on .sln file to open the solution. 
 3. Hit F5.
-4. After Unreal Editor comes up select SimGameMode in the World settings.
+4. After Unreal Editor comes up, go to the World settings and select Game Mode = SimGameMode.
 5. Make sure your environment has a Player Start component or add one. This is where the quadrotor will be placed.
 6. Hit Play button.