Add tutorial on timeseries analysis of air polution (numpy#111)

Tutorial falls in the "applications" category and highlights the use of
loadtxt to work with csv files, computing moving-window averages, and
working with statistics.

Co-authored-by: Melissa Weber Mendonça <[email protected]>

Author: Mukulikaa

README.md

@@ -25,6 +25,7 @@ or navigate to any of the documents listed below and download it individually.
 8. [Tutorial: Static Equilibrium](content/tutorial-static_equilibrium.md)
 9. [Tutorial: Plotting Fractals](content/tutorial-plotting-fractals.ipynb)
 10. [Tutorial: NumPy natural language processing from scratch with a focus on ethics](content/tutorial-nlp-from-scratch.md)
+11. [Tutorial: Analysing the impact of the lockdown on air quality in Delhi, India](content/tutorial-air-quality-analysis.md)
 
 
 ## Contributing