diff --git a/README.md b/README.md
index e69de29..16ee9ce 100644
--- a/README.md
+++ b/README.md
@@ -0,0 +1,27 @@
+## Description
+
+For some reasons, I wanted to share my computer screen to other computers in the same local network (LAN or WLAN). I could not find an easy way to do it. So, I created this small screen sharing tool in Python.
+
+In short, the computer to share screen runs this Python script that captures screenshots periodically and hosts screenshots as a web service. Other computers then browse the screenshots with any web browser.
+
+## Requirements (what I have in my own computer)
+
++ Fedora 26 + Gnome3 running on Xorg
+
++ Python 2.7
+
++ Know issue: This tool does not work with Wayland because of a <a href="https://fedoraproject.org/wiki/How_to_debug_Wayland_problems#Screen_capture_is_not_available_with_usual_apps">security reason</a>. You must use Xorg (by selecting Xorg on login).
+
+## Installation and Run
+
+1. pip install Flask-Bootstrap pyscreenshot
+
+2. In a directory, **git clone https://gitlab.com/qijungu/screenshare.git**. You will have a new directory "screenshare" with code inside.
+
+3. The command to run is "python screenshare.py [port]". Default port is 18331. Example commands are below.
+
+   python screenshare.py          # host screenshots on port 18331
+
+   python screenshare.py 80       # host screenshots on port 80
+
+4. On other computers, open a web browser and browse "http://serverip:port". For example, if the serverip is 192.168.0.101 and the service port is 18331, then other computers should browse "http://192.168.0.101:18331".
diff --git a/screenshare.py b/screenshare.py
index 44176a3..8d54823 100644
--- a/screenshare.py
+++ b/screenshare.py
@@ -23,4 +23,9 @@ def screenfeed():
 
 ### main ###
 if __name__ == '__main__':
-    app.run(host='0.0.0.0', threaded=True)
+    from sys import argv
+    if len(argv) <= 1:
+        port = 18331
+    else:
+        port = int(argv[1])
+    app.run(host='0.0.0.0', port=port, threaded=True)