add ticktext example to matlab docs

[cldougl]

Add to https://plot.ly/matlab/axes/

trace1 = struct(...
  'x', [1, 2, 3, 4], ...
  'y', [10, 15, 20, 25], ...
  'type', 'scatter');
data = {trace1};

layout = struct(...
    'xaxis', struct(...
        'ticktext', {{'one'; 'two'; 'three'; 'four'}}, ...
        'tickvals', [1, 2, 3, 4]));

response = plotly(data, struct('layout', layout, 'filename', 'axestext', 'fileopt', 'overwrite'));
plot_url = response.url