Added UART example https://github.com/raspberrypi/pico-micropython-examples/issues/19#issuecomment-783668548

uart/uart.py

@@ -0,0 +1,22 @@
+from machine import UART, Pin
+from time import sleep_us
+
+class myUART(UART):
+    def readUntil(self, termination, maxlen=-1, includeTermination=True):
+        result = ''
+        while maxlen < 0 or len(result) < maxlen:
+            if self.any():
+                #print("here")
+                result += chr(self.read(1)[0])
+                #print(result)
+                if result.endswith(termination):
+                    if not includeTermination:
+                        result = result[:-len(termination)]
+                    break
+            sleep_us(10)
+        return result
+
+uart = myUART(0, baudrate=9600, tx=Pin(0), rx=Pin(1), bits=8, parity=None, stop=1)
+
+uart.write("AT+GMR\r\n")
+print(uart.readUntil('OK',maxlen=-1, includeTermination=True))