Update readme.md with info about DM_STAGE_HOST

Author: dgolovin

README.md

@@ -137,6 +137,8 @@ and then push Ctrl + Shift + I to show ChromDevTools in current installer window
 Testing online installer
 ------------------------
 
+#### With mock server for all downloaded resourses
+
 In windows System Properties Setting Dialog add
 
     DSI_REJECT_UNAUTHORIZED=false
@@ -157,7 +159,7 @@ developers.redhat.com with download-manager links. In separate windows run
 
     node gulp-tasks/http-server.js
 
-and Then
+and then
 
     node gulp-tasks/https-server.js
 
@@ -167,6 +169,29 @@ http server always returns let you pass account information page, but if you
 plan to install and test CDK in DevStudio use your real Red Hat user name from
 developers.rdhat.com.
 
+#### With mock server for download-manager resources only
+
+In Windows System Properties Setting Dialog add
+
+    DSI_REJECT_UNAUTHORIZED=false
+    DM_STAGE_HOST=localhost
+
+to your user environment variables.
+
+Then download (VPN is Required) requirements with
+
+    gulp prefetch
+
+When download is finished run https mock servers to mimic
+developers.redhat.com with download-manager links. In separate windows execute
+
+    node gulp-tasks/https-server.js
+
+Now you are ready to test online installer without actual bits published to 
+download-manager. Start dist/win/DevelopmentSuiteInstaller-win32-x64-*.exe
+from package explorer and use it as you would normally do after release.
+
+
 Releasing the installer
 -----------------------