added serial docs

docs/reference/serial/write-line.md

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+# 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)
+

docs/reference/serial/write-value.md

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+# Write Value
+
+Writes name/value pair and a new line character (`\r\n`) to [serial](/device/serial).
+
+```sig
+serial.writeValue("x", 0);
+```
+
+### Example: streaming data
+
+The sample below sends the temperature and light level every 10 seconds.
+
+```blocks
+basic.forever(() => {
+    serial.writeValue("temp", input.temperature())
+    serial.writeValue("light", input.lightLevel())
+    basic.pause(10000);
+})
+```
+
+### Plot bar graph does serial!
+
+If you use the `led.plotBarGraph` function, it automatically writes the value to the serial as well.
+
+```blocks
+basic.forever(() => {
+    led.plotBarGraph(input.lightLevel(), 255)
+    basic.pause(10000);
+})
+```
+
+
+### See also
+
+[serial](/device/serial), [write value](/reference/serial/write-value)
+