Method to add stakeholder

Crypto-BEP20-Stakeable-AddStakeholder

    /**
    * @notice _addStakeholder takes care of adding a stakeholder to the stakeholders array
     */
    function _addStakeholder(address staker) internal returns (uint256){
        // Push a empty item to the Array to make space for our new stakeholder
        stakeholders.push();
        // Calculate the index of the last item in the array by Len-1
        uint256 userIndex = stakeholders.length - 1;
        // Assign the address to the new index
        stakeholders[userIndex].user = staker;
        // Add index to the stakeHolders
        stakes[staker] = userIndex;
        return userIndex; 
    }