Clarify repo purposes

README.md

@@ -1 +1,13 @@
 # brainglobe-workflows
+
+## Purposes of brainglobe-workflows
+
+This repository serves several related purposes
+In order of importance
+* host Python scripts for typical workflows that are easy for users to re-use (by e.g. copy-pasting contents and adapting paths or similar)
+* implement benchmarks for these workflows to ensure performance is stable as we change the code
+    * (default) run benchmarks on CI with small data
+    * (optionally) specify a configuration (as a json file) to run benchmarks on locally available, typically "real", data
+    * these configurations are not intended to be user-facing
+
+Note that to catch dependency updates breaking our code early, we additionally run and benchmark the workflows locally on a desktop machine with large example data.