docs: add configuration documentation (#816)

docs/configuration.md

@@ -0,0 +1,57 @@
+Configuration
+=============
+
+- [URLs configuration](#urls-configuration)
+  - [Base URL](#base-url)
+  - [Account URL](#account-url)
+  - [Upload URL](#upload-url)
+- [Timeout](#timeout)
+
+URLs configuration
+------------------
+
+### Base URL
+The default base URL used for making API calls to Box can be changed by calling `SetBoxApiHostUri()` method. Default value is https://api.box.com/.
+
+```c#
+var customUri = new Uri("https://custom-api-url.com");
+
+var boxConfig = new BoxConfigBuilder("clientID", "clientSecret")
+    .SetBoxApiHostUri(customUri)
+    .Build();
+```
+
+### Account URL
+The default account URL used to create OAuth authorization URL can be changed by calling `SetBoxAccountApiHostUri()` method. Default value is https://account.box.com/api/.
+
+```c#
+var customUri = new Uri("https://custom-account-url.com");
+
+var boxConfig = new BoxConfigBuilder("clientID", "clientSecret")
+    .SetBoxAccountApiHostUri(customUri)
+    .Build();
+```
+
+### Upload URL
+The default URL used for uploads can be changed by calling `SetBoxUploadApiUri()` method. Default value is https://upload.box.com/api/.
+
+```c#
+var customUri = new Uri("https://custom-upload-url.com");
+
+var boxConfig = new BoxConfigBuilder("clientID", "clientSecret")
+    .SetBoxUploadApiUri(customUri)
+    .Build();
+```
+
+Timeout
+-------
+
+The default request timeout can be changed by calling `SetTimeout()` method. Default timeout is 100 seconds.
+
+```c#
+var timeout = TimeSpan.FromSeconds(200);
+
+var boxConfig = new BoxConfigBuilder("clientID", "clientSecret")
+    .SetTimeout(timeout)
+    .Build();
+```