Append to array in json file using jq

Example from a script I wrote. Modify as needed

# Records a decision in DECISION_FILE_PATH
#
# The contents of this file can then later be used by our CI job to take
# appropriate action.
function decision {
    local environemnt="$1"
    local cluster="$2"
    local action="$3"
    local reason="$4"

    # Initialise file to the empty list if it does not exist.
    if [[ ! -f ${DECISION_FILE_PATH} ]]; then
        echo "[]" > $DECISION_FILE_PATH
    fi

    decisions=$(cat "${DECISION_FILE_PATH}")
    decision="{
        \"environment\": \"${environemnt}\",
        \"cluster\": \"${cluster}\",
        \"action\": \"${action}\",
        \"reason\": \"${reason}\"
    }"

    # Add decision object to array
    echo "${decisions}" | jq ". += [$decision]" > "${DECISION_FILE_PATH}"   
}