update README

README.md

 # PGServer
 *Work in progress, many/some features still missing!*
 
-Another PostGIS http API server  
-Upload and download geo-data, preview, filter  
+Another PostGIS http API server
+Upload and download geo-data, preview, filter
 Serve cached mapbox vector tiles (mvt), geojson, geobuf
 
 Built on [Node Express](https://expressjs.com/)
@@ -11,6 +11,34 @@ Built on [Node Express](https://expressjs.com/)
 * access to a [PostGIS](https://postgis.net) server
 * [Node and npm](https://nodejs.org/en/download/)
 
+## PostgreSQL user
+User should **only** have SELECT right on tables. You can create one as follows:
+
+```sql
+-- Create a group
+CREATE ROLE readaccess;
+
+-- Grant access to existing tables
+GRANT USAGE ON SCHEMA public TO readaccess;
+GRANT SELECT ON ALL TABLES IN SCHEMA public TO readaccess;
+
+-- Grant access to future tables
+ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO readaccess;
+
+-- Create a final user with password
+CREATE USER <user> WITH PASSWORD '<pw>';
+GRANT readaccess TO <user>;
+GRANT SELECT ON ALL TABLES IN SCHEMA public TO <user>;
+```
+
+Make sure to edit /etc/postgresql/10/main/pg_hba.conf line
+
+`local   all     all     peer`
+
+to
+
+`local   all     all     md5`
+
 ## Installation
 If you don't have git, you can donwload [a zip file](https://github.com/anneb/pgserver/archive/master.zip) of the project instead.