📝 Help contributors aroud lerna and yarn workspaces

CONTRIBUTING.md

@@ -1,10 +1,21 @@
 # Contributing
 
-* All PRs are welcome in the `develop` branch.
-* Please, stick to the repo's defined [Purpose](https://github.com/vbuch/node-signpdf#purpose) and try to write your code as readable as possible.
+* **All PRs are welcome** in the `develop` branch.
+* Please, stick to the defined [Purpose](https://github.com/vbuch/node-signpdf#purpose) of the repo and try to write your code as readable as possible.
+* [Yarn Workspaces](https://classic.yarnpkg.com/lang/en/docs/workspaces/) + [Lerna](https://lerna.js.org/) are used in this **monorepo**.
 * We do code reviews and may ask you to change things before we merge code.
 * Note that [gitmoji](https://gitmoji.carloscuesta.me/) is used in the commit messages. That's not a must but we think it's nice.
 
+## Useful commands
+
+- `$ yarn lint` - As run in your pre-commit
+- `$ yarn test` - As run in your pre-push
+- `$ ./node_modules/.bin/lerna run build` builds all the packages in their respective `dist` folders.
+- `$ ./node_modules/.bin/lerna run test --scope=@signpdf/signpdf -- --watch --coverage` runs tests in a specified package tracking coverage and watching.
+- `$ yarn workspace @signpdf/signpdf add node-forge -D` adds a `node-forge` as a dev dependency 
+of `@signpdf/signpdf`
+- `$ yarn workspace @signpdf/signpdf add @signpdf/some-new-subpackage@* -D` adds a `@signpdf/some-new-subpackage` as a dev dependency of `@signpdf/signpdf`. Note the `@*` version specifier.
+
 ## Contributors
 
 * [vbuch](https://github.com/vbuch)