Fix docs for auto_lr_find

[edenlightning]

This is the correct way to run

trainer = pl.Trainer(auto_lr_find=True)

lr_finder = trainer.tuner.lr_find(model) # Run learning rate finder

fig = lr_finder.plot(suggest=True) # Plot
fig.show()

model.hparams.learning_rate = lr_finder.suggestion()

[Borda]

@edenlightning mind share where are the wrong docs?

[SkafteNicki]

Closing this as it was solved by #3883

[thepurpleowl]

For future readers, it they stumble upon this issue,
refer the following documentation - lr_finder