tour: Add instructions to manually install and run gotour

Fix: https://github.com/golang/tour/issues/293
and many other related issues.

Change-Id: I6a8cd83e660c04a87256d94114f9f37a05c765f2
Reviewed-on: https://go-review.googlesource.com/61510
Reviewed-by: Steve Francia <spf@golang.org>
diff --git a/content/welcome.article b/content/welcome.article
index c587172..80800f3 100644
--- a/content/welcome.article
+++ b/content/welcome.article
@@ -81,6 +81,12 @@
 #appengine: 
 #appengine: 	go tool tour
 #appengine: 
+#appengine: Or, you can install and run this tour manually if you have any trouble
+#appengine: running the above command:
+#appengine: 
+#appengine:   go get golang.org/x/tour/gotour
+#appengine:   gotour
+#appengine: 
 #appengine: The tour program will open a web browser displaying
 #appengine: your local version of the tour.
 #appengine: