intro to pandas notebook about notebooks

[Tinghao724]

I have made thoroughly changes regarding the notebook. I will continue check and update it when I am working on numpy. It'd be helpful that you could give some comments for guidance.

comments:

task 1 & 2. Done
task 3. I just got a little bit confused about why using a two-step methods with loc to grab row data. Multiple indexing might be a little bit bit challenging, even though it is natural. Maybe a good stepping stone for group by methods in the future. I am not sure.
task4. I did not give it a specific section to it. However, I repeated 3 times in the notebook and used with different methods and compare the results while setting axis=1 and axis=0.

Let me know if you have any additional idea.