title: Add spelling/grammatical error to data
body: <p>Basically, I want to increase the dataset I already have, containing series of sentences, and to do so I planned to add grammatical/spelling error to each sentence in the dataset. The data set i have is completely clean, i.e, without any spelling/grammatical errors. How can that be done keeping in mind that not too many errors should be added to any particular sentence and hence prevent the change in its meaning/sense.</p>