update terminology according to data_dictionary

[kellijohnson-NOAA]

When reading through the Introduction vignette I noticed that some of the terminology that is used is inconsistent with what will be provided in the data dictionary effort. For example, indices of abundance should be survey catch per unit effort. This will be a rather large effort that should be completed after the data dictionary is published. In the mean time incremental changes can be made for words that are solidified prior to publication.