hgweb.cgi: take REPO_ROOT and REPO_NAME from env, so can be used out of the box

sys/src/cmd/hg/hgweb.cgi

@@ -1,28 +1,10 @@
 #!/bin/python
-#
-# An example CGI script to use hgweb, edit as necessary
-
-# adjust python path if not a system-wide install:
-#import sys
-#sys.path.insert(0, "/path/to/python/lib")
 
 # enable importing on demand to reduce startup time
 from mercurial import demandimport; demandimport.enable()
 
-# Uncomment to send python tracebacks to the browser if an error occurs:
-#import cgitb
-#cgitb.enable()
-
-# If you'd like to serve pages with UTF-8 instead of your default
-# locale charset, you can do so by uncommenting the following lines.
-# Note that this will cause your .hgrc files to be interpreted in
-# UTF-8 and all your repo files to be displayed using UTF-8.
-#
-#import os
-#os.environ["HGENCODING"] = "UTF-8"
-
 from mercurial.hgweb.hgweb_mod import hgweb
 import mercurial.hgweb.wsgicgi as wsgicgi
-
-application = hgweb("/path/to/repo", "repository name")
+import os
+application = hgweb(os.environ["REPO_ROOT"], os.environ["REPO_NAME"])
 wsgicgi.launch(application)