content: always display note about how documentation was rendered
Fixes github.com/golang/go/issues/37665
CI-Result: Cloud Build
<div class="Documentation">
{{.Documentation}}
<div class="Documentation-build">
- {{if not (eq .GOOS "linux")}}
<div>Documentation was rendered with GOOS={{.GOOS}} and GOARCH={{.GOARCH}}.</div>
- {{end}}
</div>
</div>
