Add -y flag for easier installation (#1024)

* Add -y flag for easier installation

* Add update command before installing

* Update README.md

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Co-authored-by: Shuanglei Tao <tsl0922@gmail.com>

README.md

@@ -37,7 +37,8 @@ ttyd is a simple command-line tool for sharing terminal over the web.
 - Install the snap: `sudo snap install ttyd --classic`
 - Build from source (debian/ubuntu):
     ```bash
-    sudo apt-get install build-essential cmake git libjson-c-dev libwebsockets-dev
+    sudo apt-get update
+    sudo apt-get install -y build-essential cmake git libjson-c-dev libwebsockets-dev
     git clone https://github.com/tsl0922/ttyd.git
     cd ttyd && mkdir build && cd build
     cmake ..