Update documents

- Add `Configuration file` section

docs/en/docs/options.md

@@ -1,4 +1,6 @@
-# Derive Options
+# Configuration
+
+## Derive options
 
 You can control the rendering behaviour via `template` attribute.
 
@@ -13,7 +15,7 @@ struct TemplateStruct {
 `template` attribute accepts the following options.
 
 - `path`: path to template file. This options is always required.
-- `escape`: Enable HTML escaping (default: `false`)
+- `escape`: Enable HTML escaping (default: `true`)
 - `delimiter`: Replace the '%' character used for the tag delimiter (default: '%')
 - `rm_whitespace`: try to strip whitespaces as much as possible without collapsing HTML structure (default: `false`). This option might not work correctly if your templates have inline `script` tag.
 
@@ -28,3 +30,32 @@ struct TemplateStruct {
     ...
 }
 ```
+
+## Configuration file
+
+Sailfish allows global and local configuration in a file named `sailfish.yml`. Sailfish looks for this file in same directory as `Cargo.toml` and all parent directories.
+If, for example, `Cargo.toml` exists in `/foo/bar/baz` directory, then the following configuration files would be scanned in this order.
+
+- `/foo/bar/baz/sailfish.yml`
+- `/foo/bar/sailfish.yml`
+- `/foo/sailfish.yml`
+- `/sailfish.yml`
+
+If a key is specified in multiple configuration files, the value in the deeper directory takes precedence over ancestor directories.
+
+If a key is specified in both configuration file and derive options, then the value specified in the derive options takes precedence over the configuration file.
+
+### Configuration file format
+
+Configuration files are written in the YAML 1.2 format. The default configuration is described below.
+
+```
+template_dir: "templates"
+escape: true
+delimiter: "%"
+
+optimization:
+    rm_whitespace: false
+```
+
+You can specify another template directory in `template_dir` option. Other options are same as derive options.

docs/en/mkdocs.yml

@@ -44,6 +44,6 @@ nav:
   - 'Welcome': 'index.md'
   - 'Installation': 'installation.md'
   - 'Getting Started': 'getting-started.md'
-  - 'Options': 'options.md'
+  - 'Configuration': 'options.md'
   - 'Syntax':
     - 'Overview': 'syntax/overview.md'