Improve help documentation for cb_add_col_attributes

[mbcann01]

Overview

At the very least, we need to document the five special attributes that cb_add_col_attributes() recognizes. Take directly from README.

The function documentation for cb_add_col_attributes() says nothing about the col_type attribute. True, it isn't a parameter, but it is a very important attribute. That needs to be may very clear. Probably in the ... section. We should probably also copy and paste some of the language from cb_add_summary_stats.

If you look at the cb_get_col_attributes() code, it looks like description, source, and col_type are attributes that aren't documented in cb_add_col_attributes(), but have special preference.

codebook()

Just needs to be way more descriptive. We should probably also copy and paste some of the language from cb_add_summary_stats.

Task list

• Document five special attributes
• Document the col_type attribute in cb_add_col_attributes
• Update the codebook help documentation - see README
• Document the package (https://roxygen2.r-lib.org/articles/rd.html#packages)