docs(readme): add section on making own formsg fork

README.md

@@ -3,3 +3,47 @@
 Builds and publishes a Docker image to 
 opengovsg/formsg-intl
 
+# Overview
+
+This repository consists of the following meaningful parts:
+
+### `replacements/`
+A minimal set of source files used to replace parts of the FormSG codebase,
+hiding or removing features specific to Singapore
+
+### `Dockerfile`
+A variation of the original `Dockerfile` in the FormSG codebase used
+to build production images. This variation deliberately installs 
+[MockPass](https://github.com/opengovsg/mockpass) to add placeholder
+certificates. These certificates are usually used by FormSG to interact
+with Singpass and Corppass, and are hence required at runtime.
+
+### `.github/workflows/ci.yml`
+A GitHub Actions workflow to:
+- copy the original FormSG codebase
+- replace some of the source code using the files in `replacements/`
+- build a Docker image using `Dockerfile`, pushing the result to Docker Hub
+
+## Creating a fork of FormSG without Singapore-specific features
+- Fork the original codebase at [opengovsg/FormSG](https://github.com/opengovsg/FormSG)
+- Clone the resulting repository onto your local machine
+- While in the directory containing your repository, clone the formsg-intl repository
+  into a subdirectory called `formsg-intl`
+```
+git clone --depth 1 [email protected]:opengovsg/formsg-intl
+```
+- Replace `Dockerfile`, and remove Singapore-specific features by replacing
+  corresponding files with equivalents using the following command: 
+```
+cp -rf formsg-intl/replacements/* .
+cp -f formsg-intl/Dockerfile .
+```
+- Once replacements are complete, remove the `formsg-intl/` directory with the command:
+```
+rm -rf formsg-intl
+```
+
+You now have a codebase of FormSG that has most of the Singapore-specific features hidden.
+note that the code implementing these features may still be present, so you are free to
+remove them, or study them to understand how you might build equivalent features in your 
+local context.