Oops.  Forgot that app/app.yaml does not exist in the SVN repo (because everyone's is different).  Added instructions for making one from the existing app/app.yaml.template file.

git-svn-id: http://soc.googlecode.com/svn/wiki@469 5fae56a1-394a-0410-ba46-5107137fd53f
diff --git a/GettingStarted.wiki b/GettingStarted.wiki
index ecea5dd..24df1ec 100644
--- a/GettingStarted.wiki
+++ b/GettingStarted.wiki
@@ -19,8 +19,36 @@
 Change directories into your SVN working copy (into the `trunk/` directory if you have
 customized your working copy).  There is currently no _build_ step for the Melange web
 application (though one will soon be needed in order to upload Melange to a Google
-App Engine instance).  The Melange web application can be started from the SVN working
-copy with this command line:
+App Engine instance).  However, you will need to create your own `app/app.yaml` file from
+the existing `app/app.yaml.template` file.  On a UNIX system, in the working copy using
+shell commands, this can be done with something like:
+
+{{{
+cp app/app.yaml.template app/app.yaml
+}}}
+
+Then, edit the newly-created `app.yaml` file with your favorite editor, changing these
+lines:
+
+{{{
+# TODO(proto): uncomment and supply a Google App Engine application instance
+# application: FIXME
+}}}
+
+to something like:
+
+{{{
+application: your-app-engine-name
+}}}
+
+where `your-app-engine-name` is the name of one of your Google App Engine slots (or
+just some made-up string if you only want to run the `dev_appserver.py` that comes
+with the
+[http://code.google.com/appengine/downloads.html Google App Engine SDK].
+
+The Melange web application can the be started from the SVN working copy with this
+command line (since `thirdparty/google_appengine` is checked into the Melange SVN
+repository because tests need it to run):
 
 {{{
 thirdparty/google_appengine/dev_appserver.py app