pybop-team#123 matrix script is working now, clean it up

scripts/ci/build_matrix.sh

@@ -3,15 +3,18 @@
 # This helper script generates a matrix for further use in the
 # scheduled/nightly builds for PyBOP, i.e., in scheduled_tests.yaml
 # It generates a matrix of all combinations of the following variables:
-# - python_version: 3.8, 3.9, 3.10, 3.11
+# - python_version: 3.X
 # - os: ubuntu-latest, windows-latest, macos-latest
-# - pybamm_version: the last four versions of PyBaMM from PyPI
+# - pybamm_version: the last four versions of PyBaMM from PyPI, excluding release candidates
+
+# To update the matrix, the variables below can be modified as needed.
 
 python_version=("3.8" "3.9" "3.10" "3.11")
 os=("ubuntu-latest" "windows-latest" "macos-latest")
 # This command fetches the last four PyBaMM versions excluding release candidates from PyPI
 pybamm_version=($(curl -s https://pypi.org/pypi/pybamm/json | jq -r '.releases | keys[]' | grep -v rc | tail -n 4 | awk '{print "\"" $1 "\"" }' | paste -sd " " -))
 
+# open dict
 json='{
   "include": [
 '
@@ -37,5 +40,4 @@ json+='
   ]
 }'
 
-# escape "" quotes with \ and print the JSON output in one line
 echo "$json" | jq -c .