title: pandas plot time series label the first point on x-axis or change major_ticks
body: <p>I have a time series plot that starts 2001-01-01 to 2020-12-31. Is there a way I can label the first point in x-axis 2001? Alternatively, can I change the major tick to every 2 years, such that it labels 2001, 2003... 2019?</p>
  <p>Sample series:</p>
  <pre><code>import numpy as np
  import pandas as pd
  
  data = np.random.rand(240)
  ser = pd.Series(data, pd.date_range(start='2001-01-31', end='2020-12-31', freq='M')) 
  </code></pre>
  <p><a href="https://i.stack.imgur.com/5L473.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5L473.png" alt="enter image description here" /></a></p>