arc42 more intro

architecture_docs/01_introduction_and_goals.md

@@ -1,9 +1,20 @@
 # Introduction And Goals
 
-Also see the top level [README.md](../README.md) for a high-level overview of the project.
+The top level [README.md](../README.md) already provides a good high-level overview of the project.
 
 Loculus is a software package to power microbial genomial databases.
 
 This is an overview of important use cases:
 
 ![Use Cases](plantuml/01_use_cases.svg)
+
+Users don't need to authenticate (given the Loculus instance is public) to view sequences and metadata.
+However, they need to authenticate to upload data (we call those users "submitters").
+A user is potentially anyone who is interested in the data, e.g. a researcher, a public health official, or a member of the public.
+Submitters will likely be researchers or lab technicians who generate the data.
+
+A maintainer is a person (or group of people) who hosts a Loculus instance.
+Depending on the needs, we imagine that Loculus could be used for example in the following scenarios:
+* a globally available database (like [Pathoplexus](https://pathoplexus.org/)),
+* a database for a research group to share the data that they generate,
+* a platform to process and analyse data from INSDC.