Doc: selecting run environment in run settings

Change-Id: I02f2bc70733e03b9b340c37019fef5d6a7af6872
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

doc/src/projects/creator-projects-settings-build.qdoc

@@ -170,7 +170,7 @@
     \section1 Build Environment
 
     You can specify the environment you want to use for building in the
-    \b{Build Environment} section. By default, the environment in which \QC
+    \gui {Build Environment} section. By default, the environment in which \QC
     was started is used and modified to include the Qt version.
     Depending on the selected Qt version, \QC automatically sets the
     necessary environment variables. You can edit existing environment

doc/src/projects/creator-projects-settings-run.qdoc

@@ -53,6 +53,28 @@
     \include qnx/creator-projects-settings-run-qnx.qdocinc
     \endif
 
+    \section1 Selecting the Run Environment
+
+    \QC automatically selects the environment used for running the application
+    based on the device type. You can edit the environment or select another
+    environment in the \gui {Run Environment} section.
+
+    You can edit existing environment variables or add, reset and unset new
+    variables.
+
+    \image qtcreator-run-environment.png "Run Environment section"
+
+    When running on the desktop, the \gui {Build Environment} is used by
+    default, but you can also use the \gui {System Environment} without the
+    additions made to the build environment. For more information, see
+    \l {Build Environment}.
+
+    To run in a clean system environment, select \gui {Clean Environment}.
+
+    When running on a mobile device connected to the development host, \QC
+    fetches information about the \gui {Device Environment} from the device.
+    Usually, it does not make sense to edit the device environment.
+
     \section1 Specifying a Custom Executable to Run
 
     If you use CMake or the generic project type in \QC, or want