Remove recommendation to use vendoring from README

Vendoring was relevant in the GOPATH days, but with Go modules, users
can refer to specific versions of Staticcheck, which also protects them
from breaking changes if using our libraries.

Author: dominikh

README.md

@@ -54,9 +54,8 @@ In addition to the aforementioned tools, this repository contains the
 libraries necessary to implement these tools.
 
 Unless otherwise noted, none of these libraries have stable APIs.
-Their main purpose is to aid the implementation of the tools. If you
-decide to use these libraries, please vendor them and expect regular
-backwards-incompatible changes.
+Their main purpose is to aid the implementation of the tools.
+You'll have to expect semiregular backwards-incompatible changes if you decide to use these libraries.
 
 ## System requirements