Mention minimum go compiler version

Also npm is required.

README.md

@@ -28,7 +28,7 @@ $ brew install yudai/gotty/gotty
 
 ## `go get` Installation (Development)
 
-If you have a Go language environment, you can install GoTTY with the `go get` command. However, this command builds a binary file from the latest master branch, which can include unstable or breaking changes.
+If you have a Go language environment, you can install GoTTY with the `go get` command. However, this command builds a binary file from the latest master branch, which can include unstable or breaking changes. GoTTY requires go1.9 or later.
 
 ```sh
 $ go get github.com/yudai/gotty
@@ -162,6 +162,8 @@ go get github.com/tools/godep
 make
 ```
 
+To build the frontend part (JS files and other static files), you need `npm`.
+
 ## Architecture
 
 GoTTY uses [xterm.js](https://xtermjs.org/) and [hterm](https://groups.google.com/a/chromium.org/forum/#!forum/chromium-hterm) to run a JavaScript based terminal on web browsers. GoTTY itself provides a websocket server that simply relays output from the TTY to clients and receives input from clients and forwards it to the TTY. This hterm + websocket idea is inspired by [Wetty](https://github.com/krishnasrinivas/wetty).