added serial docs

docs/reference/serial/write-line.md

@@ -0,0 +1,33 @@
+# Write Line
+
+Writes a string and a new line character (`\r\n`) to [serial](/device/serial).
+
+```sig
+serial.writeLine("");
+```
+
+### Example: streaming data
+
+The following example constantly checks the [compass heading](/reference/input/compass-heading) and sends the direction to serial.
+
+```blocks
+basic.forever(() => {
+    let heading = input.compassHeading()
+    if (heading < 45) {
+        serial.writeLine("N");
+    } else if (heading < 135) {
+        serial.writeLine("E");
+    }
+    else if (heading < 225) {
+        serial.writeLine("S");
+    }
+    else {
+        serial.writeLine("W");
+    }
+})
+```
+
+### See also
+
+[serial](/device/serial), [write value](/reference/serial/write-value)
+