docs: added showdown configuration document

docs/configuration.md

@@ -0,0 +1,60 @@
+You can change Showdown's default behavior via options. 
+
+## Set option
+
+### Globally
+
+Setting an option globally affects all Showdown instances.
+
+```js
+showdown.setOption('optionKey', 'value');
+```
+
+### Locally
+
+Setting an option locally affects the specified Converter object only. You can set local options via:
+
+=== "Constructor"
+
+    ```js
+    var converter = new showdown.Converter({optionKey: 'value'});
+    ```
+
+=== "setOption() method"
+
+    ```js
+    var converter = new showdown.Converter();
+    converter.setOption('optionKey', 'value');
+    ```
+
+## Get option
+
+Showdown provides both local and global methods to retrieve previously set options:
+
+=== "getOption()"
+    
+    ```js
+    // Global
+    var myOption = showdown.getOption('optionKey');
+
+    //Local
+    var myOption = converter.getOption('optionKey');
+    ```
+
+=== "getOptions()"
+
+    ```js
+    // Global
+    var showdownGlobalOptions = showdown.getOptions();
+
+    //Local
+    var thisConverterSpecificOptions = converter.getOptions();
+    ```
+
+### Get default options
+
+You can get Showdown's default options with:
+
+```js
+var defaultOptions = showdown.getDefaultOptions();
+```

mkdocs.yml

@@ -32,4 +32,6 @@ nav:
     - Donations: donations.md
   - Quickstart:
     - Quickstart: quickstart.md
-    - Compatibility: compatibility.md
+    - Compatibility: compatibility.md
+  - Configuration:
+    - Showdown options: configuration.md