title: Adding legends into a Graph made using Matplotlib and Numpy (multiple plots from a txt file)
body: <p>I had some really good help from here when I asked a question before so I thought I'd jump on again to get some help, here's my code so far:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  import os
  os.chdir("C:\Users\Chloe\Desktop")
  data=np.loadtxt("tree_rings.txt")
  for column in data.T[1:]:
      plt.plot(data[:,0],column)
  plt.title("Growth of Tree Rings Over Time")
  plt.xlabel("Year")
  plt.ylabel("Size of Tree Rings (mm)")
  plt.show()
  </code></pre>
  
  <p>How do I go about adding legends for each line in the graph, there are 3 lines (sample 1, sample 2 and sample 3), I'm mostly confused on how to specify which line corresponds to which set of data. The data is set out in 4 columns, the first is the year which corresponds to the x axis so isn't plotted and the 2nd, 3rd and 4th columns are plotted as lines on the graph. I'm really new to python so thanks in advance :)</p>