docs: improve Go binary version docs (#10942)

docs/usage/golang.md

@@ -40,11 +40,19 @@ Renovate will commit all files changed within the `vendor/` folder.
 
 ### Go binary version
 
-By default, Renovate will keep up with the very latest version of `go`.
+By default, Renovate will keep up with the latest version of the `go` binary.
 
-You can "pin" the `go` version that Renovate uses.
-Say you want Renovate to use Go version 1.14, you can do this by adding `go 1.14` to your `go.mod` file.
-We do not support pinning Go versions to a specific patch level, so you cannot use `go 1.14.12`, but you can use `go 1.14` in your `go.mod` file.
+You can force Renovate to use a specific version of Go by setting a constraint.
+As an example, say you want Renovate to use the latest patch version of the `1.16` Go binary, you'd put this in your Renovate config:
+
+```json
+  "constraints": {
+    "go": "1.16"
+  }
+```
+
+We do not support patch level versions for the minimum `go` version.
+This means you cannot use `go 1.16.6`, but you can use `go 1.16` as a contraint.
 
 ### Custom registry support, and authentication