title: Drop rows before the last True False
body: <p>I have a df like this and I want to drop everything before the last row 'isBuyer' == True and prev_isBuyer == False</p>
  <p>The row 4 is the last row that contain isBuyer == True and prev_isBuyer == False, I want to drop all the rows before that. You can see my expected result. Not sure if i'm clear enough.</p>
  <p>Some information, the last row of my df 'isBuyer'  will always be False.</p>
  <pre><code>      symbol  isBuyer prev_isBuyer
  0   DOCKUSDT     True          NaN
  1   DOCKUSDT    False         True
  2   DOCKUSDT     True        False
  3   DOCKUSDT    False         True
  4   DOCKUSDT     True        False
  5   DOCKUSDT     True         True
  6   DOCKUSDT     True         True
  7   DOCKUSDT    False         True
  8   DOCKUSDT    False        False
  9   DOCKUSDT    False        False
  10  DOCKUSDT    False        False
  11  DOCKUSDT    False        False
  12  DOCKUSDT    False        False
  13  DOCKUSDT    False        False
  14  DOCKUSDT    False        False
  15  DOCKUSDT    False        False
  </code></pre>
  <p>expected result:</p>
  <pre><code>      symbol  isBuyer prev_isBuyer
  4   DOCKUSDT     True        False
  5   DOCKUSDT     True         True
  6   DOCKUSDT     True         True
  7   DOCKUSDT    False         True
  8   DOCKUSDT    False        False
  9   DOCKUSDT    False        False
  10  DOCKUSDT    False        False
  11  DOCKUSDT    False        False
  12  DOCKUSDT    False        False
  13  DOCKUSDT    False        False
  14  DOCKUSDT    False        False
  15  DOCKUSDT    False        False
  </code></pre>