Tweak doc [ci skip]

Author: sue445

_gem/README.md

@@ -15,7 +15,7 @@ See below for details.
 [/_tools/patch_for_go_gem/](/_tools/patch_for_go_gem/)
 
 ## Usage
-### `create_go_makefile`
+### [`create_go_makefile`](https://ruby-go-gem.github.io/go-gem-wrapper/GoGem/Mkmf.html#create_go_makefile-instance_method)
 `create_go_makefile` is an extension of `create_makefile`.
 
 Add a task and hacks to build Go against the `Makefile` generated by `create_makefile`.
@@ -31,9 +31,12 @@ require "go_gem/mkmf" # Append this
 # Use create_go_makefile instead of create_makefile
 # create_makefile("example/example")
 create_go_makefile("example/example")
+
+# Pass debug flags to `go build`
+create_go_makefile("example/example", go_build_args: "-gcflags='all=-N -l'")
 ```
 
-### `GoGem::RakeTask`
+### [`GoGem::RakeTask`](https://ruby-go-gem.github.io/go-gem-wrapper/GoGem/RakeTask.html)
 Provides rake tasks for `go test` with CRuby
 
 #### Example (Without config)

_gem/lib/go_gem/rake_task.rb

@@ -40,7 +40,7 @@ module GoGem
   #         end
   #
   #         build_tag = GoGem::Util.ruby_minor_version_build_tag
-  #         sh GoGem::RakeTask.build_env_vars, "golangci-lint run --build-tags #{build_tag}"
+  #         sh GoGem::RakeTask.build_env_vars, "golangci-lint run --build-tags #{build_tag} --modules-download-mode=readonly"
   #       end
   #     end
   #   end
@@ -112,14 +112,16 @@ def self.build_env_vars
       }
     end
 
+    # Change current working dir inside `ext/<GEM_NAME>/`
+    #
     # @yield
     def within_target_dir
       Dir.chdir(target_dir) do # rubocop:disable Style/ExplicitBlockArgument
         yield
       end
     end
 
-    # @return [String]
+    # @return [String] ext dir name (e.g.`ext/<GEM_NAME>/`)
     def ext_dir
       File.join("ext", gem_name)
     end