docs: update README to use v3.1.0 (#57)

Author: felangel

README.md

@@ -18,16 +18,11 @@ This package provides lint rules for Dart and Flutter which are used at [Very Go
 
 ## Usage
 
-To use the lints, add a dependency in your `pubspec.yaml`:
+To use the lints, add as a dev dependency in your `pubspec.yaml`:
 
 ```yaml
-# If you use `package:very_good_analysis/very_good_analysis.dart`, add a normal dependency.
-dependencies:
-  very_good_analysis: ^3.0.2
-
-# Or, if you just want `analysis_options.yaml`, it can be a dev dependency.
 dev_dependencies:
-  very_good_analysis: ^3.0.2
+  very_good_analysis: ^3.1.0
 ```
 
 Then, add an include in `analysis_options.yaml`:
@@ -39,7 +34,7 @@ include: package:very_good_analysis/analysis_options.yaml
 This will ensure you always use the latest version of the lints. If you wish to restrict the lint version, specify a version of `analysis_options.yaml` instead:
 
 ```yaml
-include: package:very_good_analysis/analysis_options.3.0.1.yaml
+include: package:very_good_analysis/analysis_options.3.1.0.yaml
 ```
 
 ## Suppressing Lints