docs: add instructions for forks

README.md

@@ -71,6 +71,39 @@ yarn lerna publish
 
 This will automatically bump the version and publish the packages. It'll also publish the changelogs on GitHub for each package.
 
+## Installing from a fork on GitHub
+
+Since we use a monorepo, it's not possible to install a package from the repository URL. If you need to install a forked version from Git, you can use [`gitpkg`](https://github.com/ramasilveyra/gitpkg).
+
+First install `gitpkg`:
+
+```sh
+yarn global add gitpkg
+```
+
+Then follow these steps to publish and install a forked package:
+
+1. Fork this repo to your account and clone the forked repo to your local machine
+1. Open a Terminal and `cd` to the location of the cloned repo
+1. Run `yarn` to install any dependencies
+1. If you want to make any changes, make them and commit
+1. Now `cd` to the package directory that you want to use (e.g. `cd packages/stack` for `@react-navigation/stack`)
+1. Run `gitpkg publish` to publish the package to your repo
+
+After publishing, you should see something like this:
+
+```sh
+Package uploaded to git@github.com:<user>/<repo>.git with the name <name>
+```
+
+You can now install the dependency in your project:
+
+```sh
+yarn add <user>/<repo>.git#<name>
+```
+
+Remember to replace `<user>`, `<repo>` and `<name>` with right values.
+
 <!-- badges -->
 
 [build-badge]: https://img.shields.io/circleci/project/github/react-navigation/navigation-ex/master.svg?style=flat-square