docs: fix setup instructions by requiring plugins block (#326)

Co-authored-by: Illia Aihistov <illia.aihistov-us@solid.software>

Author: solid-illiaaihistov

README.md

@@ -21,23 +21,13 @@ dev_dependencies:
 
 Enable the plugin and include `solid_lints` in your project's top-level `analysis_options.yaml`:
 
-### Option 1: Using the `plugins` block
-
 ```yaml
 include: package:solid_lints/analysis_options.yaml
 
 plugins:
   solid_lints:
 ```
 
-### Option 2: Using the top-level `solid_lints` block
-
-```yaml
-include: package:solid_lints/analysis_options.yaml
-
-solid_lints:
-```
-
 Also, you can use a specialized rule set designed for Dart tests.
 Add an `analysis_options.yaml` file under the `test/` directory, and include the ruleset: