[release-branch.go1.4] go-tour/content/welcome.article: update restrictions of the playground.

««« CL 182390043 / 7d6c480ac226
go-tour/content/welcome.article: update restrictions of the playground.

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/182390043
»»»

LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://golang.org/cl/177700043
diff --git a/content/welcome.article b/content/welcome.article
index b7084f7..4f47d30 100644
--- a/content/welcome.article
+++ b/content/welcome.article
@@ -72,7 +72,7 @@
 #appengine: 
 #appengine: - In the playground the time begins at 2009-11-10 23:00:00 UTC (determining the sigificance of this date is an exercise for the reader). This makes it easier to cache programs by giving them deterministic output.
 #appengine: 
-#appengine: - There are also limits on execution time and on CPU and memory usage, and the program is restricted to running in a single thread (but may use many goroutines).
+#appengine: - There are also limits on execution time and on CPU and memory usage, and the program cannot access external network hosts. 
 #appengine: 
 #appengine: The playground uses the latest stable release of Go.
 #appengine: