update README

README.md

@@ -1,2 +1,35 @@
 # pg-rad
-Primary Gamma RADiation landscape
+Primary Gamma RADiation landscape - Development
+
+## Clone
+```
+git clone https://github.com/pim-n/pg-rad
+cd pg-rad
+git checkout dev
+```
+
+or
+
+```
+git@github.com:pim-n/pg-rad.git
+cd pg-rad
+git checkout dev
+```
+
+## Dependencies / venv
+
+With Python verion `>=3.12.4`, create a virtual environment and install pg-rad.
+
+```
+python3 -m venv .venv
+source .venv/bin/activate
+(venv) pip install -e .[dev]
+```
+
+## Tests
+
+Tests can be run with `pytest` from the root directory of the repository.
+
+```
+(venv) pytest
+```