Update readme with new security metadata flag

Update the readme file with the flag for includeFieldSecurityMetadata in the Markdown section. Include the default as well as the type of input.

Author: williamsalexisSFDC

README.md

@@ -124,6 +124,7 @@ apexdocs changelog --previousVersionDir force-app-previous --currentVersionDir f
 | `--linkingStrategy`        | N/A   | The strategy to use when linking to other classes. Possible values are `relative`, `no-link`, and `none`                                                                                                 | `relative`       | No       |
 | `--customObjectsGroupName` | N/A   | The name under which custom objects will be grouped in the Reference Guide                                                                                                                               | `Custom Objects` | No       |
 | `--triggersGroupName`      | N/A   | The name under which triggers will be grouped in the Reference Guide                                                                                                                                     | `Triggers`       | No       |
+| `--includeFieldSecurityMetadata`      | N/A   | Whether to include the compliance category and security classification for fields in the generated files.                                                                                                                                     | `false`       | No       |
 
 ##### Linking Strategy