Updated FAQ (markdown)

FAQ.md

@@ -29,6 +29,7 @@
   - [How to know the type of a value?](#how-to-know-the-type-of-a-value)
   - [Can I access to object member by its index, instead of its key?](#can-i-access-to-object-member-by-its-index-instead-of-its-key)
   - [How to fix error "Ambiguous overload for 'operator='"](#how-to-fix-error-ambiguous-overload-for-operator)
+  - [Why JsonVariant cannot be converted to char?](#why-jsonvariant-cannot-be-converted-to-char)
 
 <!-- /MarkdownTOC -->
 
@@ -826,3 +827,23 @@ ssid = network["ssid"].as<String>();
 ```
 
 See issue [#118](https://github.com/bblanchon/ArduinoJson/issues/118), [#146](https://github.com/bblanchon/ArduinoJson/issues/146) and [#197](https://github.com/bblanchon/ArduinoJson/issues/197).
+
+### Why JsonVariant cannot be converted to char?
+
+The `char` type has been intentionally disabled to avoid an ambiguity.
+
+Imagine you have this input: `{'time':'8'}`; what should be the value of `root["time"]` as a `char`?
+
+I see two possible answers:
+
+* Either you see `char` as an integer; in that case, the result should be `8`.
+* Or you see `char` as a character; in that case, the result should be `56` (the ASCII code of character `8`)
+
+Since there is not good answer to this question, the `char` type has been disabled, but `unsigned char` and `signed char` works as integers.
+
+However, I highly encourage you to use `char` to store characters, and `int8_t` or `uint8_t` to store integers. If you compile with Arduino, you also have the [byte](https://www.arduino.cc/en/Reference/Byte) type.
+
+See also:
+
+* [API Reference: JsonVariant::as()](https://github.com/bblanchon/ArduinoJson/wiki/API%20Reference#jsonvariantas)
+* Issues [#337](https://github.com/bblanchon/ArduinoJson/issues/337) and [#370](https://github.com/bblanchon/ArduinoJson/issues/370)