Update README.md (#6859)

Updated information for .swagger-codegen-ignore support via IntelliJ plugin, and path override.

Author: jimschubert

README.md

@@ -462,6 +462,10 @@ src/IO.Swagger.Test/Model/AnimalFarmTests.cs
 
 The `.swagger-codegen-ignore` file must exist in the root of the output directory.
 
+Upon first code generation, you may also pass the CLI option `--ignore-file-override=/path/to/ignore_file` for greater control over generated outputs. Note that this is a complete override, and will override the `.swagger-codegen-ignore` file in an output directory when regenerating code.
+
+Editor support for `.swagger-codegen-ignore` files is available in IntelliJ via the [.ignore plugin](https://plugins.jetbrains.com/plugin/7495--ignore).
+
 ### Customizing the generator
 
 There are different aspects of customizing the code generator beyond just creating or modifying templates.  Each language has a supporting configuration file to handle different type mappings, etc: