title: cannot build table with PySimpleGUI
body: <p>I would like for tab 2 to show a table of all existing reservations. </p>
  
  <p>I have tried making the dataframe a string and then a list. </p>
  
  <pre><code>import pandas as pd
  from pandas import DataFrame
  
  
  
  #create dataframe to simulate databse with names and dates
  data = {'Name':  ['Joe Smith', 'Jason Leary','Bill Murray'],
          'Start Date': ['2019/10/01', '2019/11/01','2019/12/01'],
          'End Date': ['2019/10/15', '2019/11/15','2019/12/15']
          }
  df = pd.DataFrame (data, columns = ['Name','Start Date','End Date'])
  Data_Table = df.to_string()
  
  
  
  
  # Stuff inside window
  tab1_layout = [
      [sg.Text('The Scheduler')], 
      [sg.Combo(name, size=(30,4), enable_events=True)],
      [sg.Combo(reason, size=(30,4), enable_events=True)],
      [sg.T('Start Date')],
            [sg.In('', size=(10,1), key='input1')],
            [sg.CalendarButton('Choose Start Date', target='input1', key='date1',format='%Y/%m/%d')],
      [sg.T('End Date')],
            [sg.In('', size=(10,1), key='input2')],
            [sg.CalendarButton('Choose End Date', target='input2', key='date2', format='%Y/%m/%d')],
      [sg.Button('Submit')]]
  
  # create a table to show names and dates with an export to CSV button
  tab2_layout = [[sg.Table(values=Data_Table, max_col_width=25, background_color='lightblue',
                          auto_size_columns=True, justification='right', alternating_row_color='blue', key='_table_')],
            [sg.Button('Update')]]
  
  
  
  tab3_layout = [[sg.T('This is inside tab 3')],
                 [sg.In(key='_in3_')]]
  # create the window
  layout = [[sg.TabGroup([[sg.Tab('Scheduler', tab1_layout,  key='_mykey_'),
                           sg.Tab('Schedule', tab2_layout),
                           sg.Tab('Admin', tab3_layout)]],
                           key='_group2_', title_color='darkgrey',
                           selected_title_color='black', tab_location='topleft')]]
  
  window = sg.Window('My window with tabs', default_element_size=(30,1)).Layout(layout)
  
  # event loop to process events and get the values of inputs
  while True:      
      event, values = window.Read() 
      print(event, values)       
      if event in (None, 'Exit'):      
          break 
       if event == 'Update':
          window.FindElement('_table_').Update( row_colors=((8,'white', 'red'), (9,'black')))
  
  window.Close()
  </code></pre>
  
  <p>I would like for a table to show on tab 2 with existing reservations. Ultimately this will come from a db but for now I have created a pd.DataFrame.</p>
  
  <p>The error is 
  TclError: Invalid column index<br>
  But I have tried strings and lists.</p>