docs(development): Avoid test failure (sqlc-dev#3235)

Add sqlc-gen-json installation step to 
avoid "error generating code: process: sqlc-gen-json not found"
when tests running.

Author: zawataki

docs/guides/development.md

@@ -8,6 +8,12 @@ For local development, install `sqlc` under an alias. We suggest `sqlc-dev`.
 go build -o ~/go/bin/sqlc-dev ./cmd/sqlc
 ```
 
+Install `sqlc-gen-json` to avoid test failure.
+
+```
+go build -o ~/go/bin/sqlc-gen-json ./cmd/sqlc-gen-json
+```
+
 ## Running Tests
 
 ```