README: suggest go run instead of go build

Using go run does not leave a binary in the working directory.
This is possible now that golang.org/issue/22726 is resolved.

Change-Id: I63cd28bdb66673262fa45e56dc2e8ac39a0fa1a7
Reviewed-on: https://go-review.googlesource.com/c/blog/+/216657
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/README.md b/README.md
index e98ea0d..fcacf6d 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,7 @@
 To run the blog server locally:
 
 ```
-go build && ./blog -reload
+go run . -reload
 ```
 
 and then visit [http://localhost:8080/](http://localhost:8080) in your browser.