Add env variables to sprint setup instructions (#1654)

Author: maxrjones

README-v3.md

@@ -14,6 +14,14 @@ git remote add upstream https://github.com/zarr-developers/zarr-python
 git fetch upstream
 git checkout --track upstream/v3
 ```
+## Set the environment variables for V3
+
+There are a couple environment variables required for enabling V3:
+
+```
+export ZARR_V3_EXPERIMENTAL_API=1
+export ZARR_V3_SHARDING=1
+```
 
 ## Set up your environment
 

pyproject.toml

@@ -93,6 +93,7 @@ extra-dependencies = [
 [tool.hatch.envs.test.scripts]
 run-coverage = "pytest --cov-config=pyproject.toml --cov=pkg --cov=tests"
 run = "run-coverage --no-cov"
+run-verbose = "run-coverage --verbose"
 
 [tool.ruff]
 line-length = 100