Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]).
Return the running sum of nums.
 
Please complete the following python code precisely:
```python
class Solution:
    def runningSum(self, nums: List[int]) -> List[int]:
```