docs: update docs

README.md

@@ -1,2 +1,18 @@
-# openxpki-installer
+# OpenXPKI Installer
 Simple bash script to install OpenXPKI on Debian
+
+## How to Use
+```bash
+$ sudo su
+$ git clone https://github.com/daffainfo/openxpki-installer
+$ cd openxpki-installer
+$ mv install.sh /root/
+$ bash install.sh
+```
+After install, go to https://YOUR_IP/openxpki/
+
+## Prerequisite
+- Debian 10
+
+## Reference
+- https://openxpki.readthedocs.io/en/stable/quickstart.html