README: change links to use go.dev

Change-Id: I22140fb3eed744398c2f9f158e3ed76851ccb8f5
Reviewed-on: https://go-review.googlesource.com/c/gollvm/+/625715
Reviewed-by: Than McIntosh <thanm@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>

README.md

diff --git a/README.md b/README.md
index 1ba6551..f6951c9 100644
--- a/README.md
+++ b/README.md
@@ -256,7 +256,7 @@
 
 ## How can I go about contributing to gollvm? <a name="contributing"></a>
 
-Please see the Go project guidelines at [https://golang.org/doc/contribute.html](https://golang.org/doc/contribute.html). Changes to [https://go.googlesource.com/gollvm](https://go.googlesource.com/gollvm) can be made by any Go contributor; for changes to gofrontend see [the gccgo guidelines](https://golang.org/doc/gccgo_contribute.html).
+Please see the Go project guidelines at [https://go.dev/doc/contribute](https://go.dev/doc/contribute). Changes to [https://go.googlesource.com/gollvm](https://go.googlesource.com/gollvm) can be made by any Go contributor; for changes to gofrontend see [the gccgo guidelines](https://go.dev/doc/gccgo_contribute.html).
 
 ## Is gollvm a replacement for the main Go compiler? (gc) <a name="replacegc"></a>