docs: Roadmap (#110)

# Changes

Adds brief roadmap to project readme.

# Associated issue

N/A

# How to test

Review new 'Roadmap' in project readme.

# Checklist

- [x] I have performed a self-review of my own code
- [x] I have made sure that my PR is easy to review (not too big,
includes comments)
- [x] I have made updated relevant documentation files (in project
README, docs/, etc)
- ~~I have added a decision log entry if the change affects the
architecture or changes a significant technology~~
- ~~I have notified a reviewer~~

<!-- Please strike through and check off all items that do not apply
(rather than removing them) -->

README.md

@@ -14,6 +14,16 @@
 
 \* We'll leave the choice for a JS framework and strategy for styling to developers using Head Start for their project.
 
+## Roadmap
+
+Current status: Head Start is suitable for internal use by De Voorhoede.
+
+- [v1](https://github.com/voorhoede/head-start/issues?q=is%3Aissue+is%3Aopen+label%3A%22v1%22+): all common website functionality for use by De Voorhoede.
+- [v1 public](https://github.com/voorhoede/head-start/issues?q=is%3Aissue+is%3Aopen+label%3A%22v1+public%22+): extend setup and documentation to be suitable for use outside De Voorhoede.
+- [v2](https://github.com/voorhoede/head-start/issues/77): ideas for Head Start as starterkit for websites & web apps (maybe, someday).
+
+Progress can also be tracked on the [Head Start project board](https://github.com/orgs/voorhoede/projects/5).
+
 ## Architecture
 
 The site is created as lightweight progressively enhanced website connected to a headless CMS: