go.blog: update tags

This makes the articles cross-reference each other better.
In particular, I added the "technical" tag for in-depth technical
posts.

R=bradfitz, r
CC=golang-dev
https://golang.org/cl/9960043
diff --git a/content/the-app-engine-sdk-and-workspaces-gopath.article b/content/the-app-engine-sdk-and-workspaces-gopath.article
index be40a2a..873883a 100644
--- a/content/the-app-engine-sdk-and-workspaces-gopath.article
+++ b/content/the-app-engine-sdk-and-workspaces-gopath.article
@@ -1,6 +1,6 @@
 The App Engine SDK and workspaces (GOPATH)
 9 Jan 2013
-Tags: appengine, build, gopath
+Tags: appengine, tools, gopath
 
 Andrew Gerrand