Fix replace directive in local development guide (#880)

README.md

@@ -222,7 +222,7 @@ go 1.19
 require github.com/hugo-toha/toha/v4 v4.0.1-0.20231229170427-d3968ca711ef // indirect
 
 replace(
-    github.com/hugo-toha/toha/v4 => github.com/<your-github-user>/toha <git branch>
+    github.com/hugo-toha/toha/v4 => github.com/<your-github-user>/toha/v4 <git branch>
 )
 ```