Add README

README.md

+# Mittelab main website
+
+This is Mittelab's main website (the one behind [www.mittelab.org](https://www.mittelab.org)).
+
+## How to build
+
+To build and make changes, you're going to need:
+* pipenv
+* nodejs
+* npm
+* imagemagick (for thumbnails)
+
+Once you have that, you can run:
+```shell
+pipenv install
+pipenv run lektor server -f webpack
+```
+
+Once the build finishes, you can open [http://localhost:5000](http://localhost:5000) and press on the pencil icon to
+make changes. Once you're satisfied, open a branch, commit your changes **with a meaningful commit message** and open a
+pull request!