Improve documentation of correction bar

[cboulanger]

The current documentation of the Concordance view is a bit hard to understand because it does not explain the individual parts of the UI. Could you add a bit more details on what "Toggle selection", "Set correction" and "Correct Selected" do? Also, how do I tell Pocoweb that a word is correct as recognized and can be removed from the list of "suspicious words"? I assume that this can be done with these buttons, but am not sure which/how.

Thank you.