Improve README code examples for mobile readability

Add group: :test to the Gemfile installation snippet. Break long
code example lines so they don't require horizontal scrolling on
small screens.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: thiagoa

README.md

@@ -45,7 +45,7 @@ aligned as the design changes.
 Add to your Gemfile:
 
 ```ruby
-gem "duck_typer"
+gem "duck_typer", group: :test
 ```
 
 Then run:
@@ -109,7 +109,11 @@ classes share compatible interfaces:
 
 ```ruby
 def test_payment_processors_have_compatible_interfaces
-  assert_interfaces_match [StripeProcessor, PaypalProcessor, BraintreeProcessor]
+  assert_interfaces_match [
+    StripeProcessor,
+    PaypalProcessor,
+    BraintreeProcessor
+  ]
 end
 ```
 
@@ -131,6 +135,19 @@ assert_interfaces_match [StripeProcessor, PaypalProcessor],
 This is useful if your class implements multiple interfaces, in
 which case you can write an assertion for each.
 
+To enforce that positional argument names also match (strict
+mode), pass `strict: true`:
+
+```ruby
+assert_interfaces_match [StripeProcessor, PaypalProcessor],
+  strict: true
+```
+
+By default, positional argument names are ignored — only their
+count and kind (required, optional, rest) are compared. In strict
+mode, names must match exactly. Keyword argument names always
+matter regardless of this setting.
+
 ### RSpec
 
 Require the RSpec integration in your `spec_helper.rb`:
@@ -147,21 +164,32 @@ share compatible interfaces:
 ```ruby
 RSpec.describe "payment processors" do
   it "have compatible interfaces" do
-    expect([StripeProcessor, PaypalProcessor, BraintreeProcessor]).to have_matching_interfaces
+    expect([StripeProcessor, PaypalProcessor, BraintreeProcessor])
+      .to have_matching_interfaces
   end
 end
 ```
 
 For class-level interfaces, pass `type: :class_methods`:
 
 ```ruby
-expect([StripeProcessor, PaypalProcessor]).to have_matching_interfaces(type: :class_methods)
+expect([StripeProcessor, PaypalProcessor])
+  .to have_matching_interfaces(type: :class_methods)
 ```
 
 To check only a subset of methods, use `methods:`:
 
 ```ruby
-expect([StripeProcessor, PaypalProcessor]).to have_matching_interfaces(methods: %i[charge refund])
+expect([StripeProcessor, PaypalProcessor])
+  .to have_matching_interfaces(methods: %i[charge refund])
+```
+
+To enforce that positional argument names also match, pass
+`strict: true`:
+
+```ruby
+expect([StripeProcessor, PaypalProcessor])
+  .to have_matching_interfaces(strict: true)
 ```
 
 #### Shared example
@@ -184,23 +212,30 @@ Then use it in your specs:
 
 ```ruby
 RSpec.describe "payment processors" do
-  it_behaves_like "an interface", [StripeProcessor, PaypalProcessor, BraintreeProcessor]
+  it_behaves_like "an interface", [
+    StripeProcessor,
+    PaypalProcessor,
+    BraintreeProcessor
+  ]
 end
 ```
 
-The same `type:` and `methods:` options are supported:
+The same `type:`, `methods:`, and `strict:` options are supported:
 
 ```ruby
 it_behaves_like "an interface", [StripeProcessor, PaypalProcessor],
   type: :class_methods,
-  methods: %i[charge refund]
+  methods: %i[charge refund],
+  strict: true
 ```
 
 ## Limitations
 
-DuckTyper checks the **structure** of public method signatures
-— the number of parameters, their kinds (required, optional,
-keyword, rest, block), and keyword argument names. It does not
+By default, DuckTyper checks the **structure** of public method
+signatures — the number of parameters, their kinds (required,
+optional, keyword, rest, block), and keyword argument names. In
+strict mode, positional argument names are also compared. It does
+not
 verify the following, which should be covered by your regular
 test suite: