Add info on how to build.

README.md

@@ -15,3 +15,19 @@ container) or a thing (no location ID, parent container). For every
 # Functionality
 Right now the app decodes a QR code, chen the user can add more metadata
 and finally save a *thing* in the database.
+
+# How to install
+Install prerequisites, then run:
+```
+$ pipenv install
+$ npm install --dev
+$ npm run build
+$ pipenv run ./manage.py migrate
+$ pipenv run ./manage.py runserver 8000
+```
+
+## Prerequisites
+`invman` needs the following software installed (apart from the one defined in `Pipfile`/`packages.json`):
+* PostgreSQL > 10
+* PostGIS
+* GDAL
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