chore: add dual-remote helper workflow

CONTRIBUTING.md

@@ -34,6 +34,30 @@ Rule:
 
 Do not let a customer deployment track `develop` directly.
 
+## Dual Remote Workflow
+This repository now has two different Git remotes with different purposes:
+- `origin`: the normal GitHub product remote
+- `tubco`: the TUBCO customer remote
+
+Use the helper command to avoid mixing them up:
+
+```bash
+./scripts/git_remote_target.sh status
+```
+
+Common commands:
+
+```bash
+./scripts/git_remote_target.sh push-origin
+./scripts/git_remote_target.sh push-tubco release/tubco-v1
+./scripts/git_remote_target.sh set-own-identity
+./scripts/git_remote_target.sh set-tubco-identity
+```
+
+Default rule:
+- normal product work goes to `origin`
+- TUBCO pushes happen only when explicitly requested
+
 ## Current Delivery Model
 - GitHub Actions is used for CI
 - the current test server is local/LAN-only