Update contribution

Author: jeromewu

apps/website/docs/contribution/core.md

@@ -1 +1,36 @@
 # @ffmpeg/core
+
+To build @ffmpeg/core, make sure your docker is version 23.0+ as
+[buildx](https://docs.docker.com/build/architecture/) is adopted. Also
+You will need to install `make` to run build scripts.
+
+## Build
+
+Dev Build (single thread):
+```bash
+$ make dev
+```
+
+Dev Build (multithread):
+```bash
+$ make dev-mt
+```
+
+Prodution Build (single thread):
+```bash
+$ make prd
+```
+
+Prodution Build (multithread):
+```bash
+$ make prd-mt
+```
+
+> Each build might take around 1 hour depends on the spec of your machine,
+> subsequent builds are faster as most layers are cached.
+
+The output file locates at **/packages/core** or **/packages/core-mt**.
+
+## Publish
+
+Simply run `npm publish` under **packages/core** or **/packages/core-mt**.

apps/website/docs/contribution/ffmpeg.md

@@ -1 +1,27 @@
 # @ffmpeg/ffmpeg
+
+The source code of @ffmpeg/ffmpeg locates at **/packages/ffmpeg**.
+
+## Development
+
+```bash
+$ npm run dev
+```
+
+## Build
+
+Transpile Typescript to JavaScript.
+
+```bash
+$ npm run build
+```
+
+## Lint
+
+```bash
+$ npm run lint
+```
+
+## Publish
+
+Simply run `npm publish` under **packages/ffmpeg**.

apps/website/docs/contribution/util.md

@@ -1 +1,27 @@
 # @ffmpeg/util
+
+The source code of @ffmpeg/util locates at **/packages/util**.
+
+## Development
+
+```bash
+$ npm run dev
+```
+
+## Build
+
+Transpile Typescript to JavaScript.
+
+```bash
+$ npm run build
+```
+
+## Lint
+
+```bash
+$ npm run lint
+```
+
+## Publish
+
+Simply run `npm publish` under **packages/util**.