Added example with Docker and Flask (#519)

* Added example with Docker and Flask

* set flask debug flag to False

* new line at the end of file

* format with black

---------

Co-authored-by: Ricardo Sanchez Alba <r2sanchezalba@gmail.com>

examples/docker-flask/app.py

@@ -0,0 +1,22 @@
+import escpos
+from escpos.printer import *
+from flask import Flask, jsonify, request, redirect, session, url_for
+import sys
+from io import BytesIO
+
+# Initialize Flask app
+app = Flask(__name__)
+
+
+@app.route("/", methods=["GET"])
+def do_print():
+    # p = Usb(0x04b8, 0x0e28, 0)
+    p = CupsPrinter(host="localhost", port=631, printer_name="TM-T20III")
+    p.text("Hello World\n")
+    p.cut()
+    p.close()
+    return "OK"
+
+
+if __name__ == "__main__":
+    app.run(debug=False, host="0.0.0.0", port=9999)