docs: develop external projects

README.md

@@ -115,6 +115,45 @@ it has the git dependency on [typst](https://github.com/typst/typst).
 
 See [Documentation](https://myriad-dreamin.github.io/typst.ts/cookery).
 
+### Develop projects along with a local built typst.ts
+
+You can add your owned projects to the `projects` folder, so that yarn workspace will
+automatically identify your project.
+
+##### Example: link a project by git submodule
+
+To develop core external projects, e.g. `typst-preview`, you could initialize it
+by command:
+
+```shell
+git submodule update --init --checkout projects/typst-preview
+```
+
+##### Example: build and run
+
+Ensured that you have [built typst.ts from
+source](#build-from-source-and-check), you can build and run the project by
+(typst-preview as a example):
+
+```shell
+# install dependencies for project
+yarn install --pure-lockfile
+# build typst-preview and its dependencies
+turbo build --filter=typst-preview
+@myriaddreamin/typst-ts-renderer:build: cache hit, replaying logs bc0a0b151bd8eb6d
+@myriaddreamin/typst.ts:build: cache hit, replaying logs 729cb43a3242b80
+typst-preview-frontend:build: cache miss, executing 5ae30471e8957877
+typst-preview-frontend:build: ...
+typst-preview-frontend:build: ✓ built in 1.25s
+typst-preview-frontend:build: Done in 4.57s.
+typst-preview:build: cache miss, executing a1bd8ca8233f8a0c
+typst-preview:build: ...
+typst-preview:build: ✓ built in 1.01s
+typst-preview:build: Done in 3.73s.
+```
+
+The project (typst-preview as a example) will cache and use the local built packages.
+
 ### Build from source and check
 
 Note: you could build from source with/without wasm-pack.