add two small aspects for filename description

Author: oliverrahner

src/docs/configuration.md

@@ -106,7 +106,7 @@ Each content entry can define the following keys:
 | **`type`**| `string` | **Required**. `collection` or `file`, depending on whether the content entry is a collection of files with an identical schema (e.g. blog posts) or a single file (e.g. home page). |
 | **`path`** | `string` | **Required**. Path to the folder where the files are stored if it's a collection (e.g. `path: src/posts`, otherwise the path to the single file (e.g. `path: src/index.md`). |
 | **`fields`** | `string` | The list of fields defining the schema of the content entry (e.g. title, date, author, body, etc). [See the "Fields" section below](#fields). |
-| **`filename`** | `string` | The pattern to generate the filename when creating a new file. You can use the value of any field (e.g. `fields.title`) including nested values (e.g. `fields.tags[0].label`). You can also use a few date tokens (`{year}`, `{month}`, `{day}`) and time (`{hour}`, `{minute}`, `{second}`) and `{primary}` for the primary field as defined in the `view` key. By default this is set to `'{year}-{month}-{day}-{primary}.md'`. |
+| **`filename`** | `string` | The pattern to generate the filename when creating a new file. This also defines how files are looked up. You can use the value of any field (e.g. `{{fields.title}}`) including nested values (e.g. `{{fields.tags[0].label}}`). You can also use a few date tokens (`{year}`, `{month}`, `{day}`) and time (`{hour}`, `{minute}`, `{second}`) and `{primary}` for the primary field as defined in the `view` key. By default this is set to `'{year}-{month}-{day}-{primary}.md'`. |
 | **`exclude`** | `array` | An array of files to exclude from the collection (e.g. `[ README.md ]`). This is only valid for collections.
 | **`view`** | `object` | **Only valid for collections**. This object defines the various options for the collection view; visible fields, sorting options and defaults, fields indexed for the search... [See the "View" section below](#view). |
 | **`format`** | `string` | The format of the file, used to set up the editor to edit the content: `yaml-frontmatter`, `json-frontmatter`, `toml-frontmatter`, `yaml`, `json`, `toml`, `datagrid`, `code` or `raw`. It defaults to `yaml-frontmatter`. |