[USER (data scientist)]: Sweet! Finally, let's make that heatmap with seaborn and matplotlib to visualize the demand.  Please generate a PNG image to visualize the heatmap of affordable housing demand by suburb and year in the dataframe 'melbourne_housing'.
My template of code snippet is:

---BEGIN CODE TEMPLATE---

import pandas as pd
import pickle
import seaborn as sns   
import matplotlib.pyplot as plt 

melbourne_housing = pd.read_csv("melb_data.csv") 

# YOUR SOLUTION BEGIN:
<code1>
[GENERATE YOUR CODE]
</code1>
# YOUR SOLUTION END:

plt.savefig('./pred_result/heat_map.png')
plt.show()

---END CODE TEMPLATE---

[YOU (AI assistant)]: Absolutely! Here's the code to create a heatmap using seaborn and matplotlib: 
