Add Linux stubs

README.md

@@ -34,7 +34,7 @@ On macOS, use Homebrew.
 brew install --HEAD FiloSottile/mkcert/mkcert
 ```
 
-On Linux (support coming soon!), use [the pre-built binaries](https://github.com/FiloSottile/mkcert/releases), or build from source.
+On Linux (install support coming soon!), use [the pre-built binaries](https://github.com/FiloSottile/mkcert/releases), or build from source.
 
 ```
 $ git clone https://github.com/FiloSottile/mkcert

truststore_linux.go

@@ -0,0 +1,16 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"log"
+	"path/filepath"
+)
+
+func (m *mkcert) installPlatform() {
+	log.Fatalf("-install is not yet supported on Linux 😣\nYou can manually install the root certificate at %q in the meantime.", filepath.Join(m.CAROOT, rootName))
+}
+
+func (m *mkcert) uninstallPlatform() {}