Replaced 'goinstall' with 'go get'

It seems like 'goinstall' is now 'go get', but getting that piece of information from web search is not too easy. Hope this would save other n00bs' time.

README.md

@@ -5,15 +5,15 @@ This is a memcache client library for the Go programming language
 
 ## Installing
 
-### Using *goinstall*
+### Using *go get*
 
-    $ goinstall github.com/bradfitz/gomemcache/memcache
+    $ go get github.com/bradfitz/gomemcache/memcache
 
 After this command *gomemcache* is ready to use. Its source will be in:
 
     $GOROOT/src/pkg/github.com/bradfitz/gomemcache/memcache
 
-You can use `goinstall -u -a` for update all installed packages.
+You can use `go get -u -a` for update all installed packages.
 
 ### Using *git clone* command: