Vignette on the add_*/remove_*/update_*, adjust_* and tidy functions

[rachlobay]

Here's a vignette that goes over how to use the add/remove/update, adjust and tidy functions that were recently added to the package.

[dajmcdon]

I made some suggestions for simplicity. Please try to apply the same throughout the vignette (I suspect I got many, but not all).

Once you're done, you can merge.

[dajmcdon]

Can you add carriage returns so that this line breaks at 80 characters? Makes reviewing and editing much easier. Same for much of the below.

[dajmcdon]

for functions, it's better to end them with open+close parenthesis. I think here, these are all "objects", so it doesn't need that, but maybe clearer then to add "objects" in the sentence.

[dajmcdon]

more functions.

[dajmcdon]

Suggested change

	Now, while we checked what happens to the above `epi_recipe` if we remove it, note that we did not actually store that change to `wf` (using the assignment operator `<-`). Hence, our `epi_workflow` remains unchanged.
	Now, while we checked what happens to the above `epi_recipe` if we remove it, note that we did not actually store that change to `wf`.

[dajmcdon]

For example:

Suggested change

	In the context of pre-processing, the goal of the update functions is to add/remove/update an `epi_recipe` or a step in it. For this, we have `add_epi_recipe`, `update_epi_recipe`, and `remove_epi_recipe` to add/update/remove an entire `epi_recipe` in an `epi_workflow` as well as `adjust_epi_recipe` to adjust a particular step in an `epi_recipe` or `epi_workflow` by the step number or name. For a model, one may `add_model`, `update_model`, or `remove_model` in an `epi_workflow`. For post-processing, where the goal is to update a frosting object or a layer in it, we have `add_frosting`, `remove_frosting`, and `update_frosting` to add/update/remove an entire `frosting` object in an `epi_workflow` as well as `adjust_frosting` to adjust a particular layer in a `frosting` or `epi_workflow` by its number or name. A summary of the function uses by processing step is shown by the following table:
	In the context of pre-processing, the goal of the update functions is to add/remove/update an
	`epi_recipe` or a step in it. For this, we have `add_epi_recipe()`, `update_epi_recipe()`, and `remove_epi_recipe()` to alter an entire `epi_recipe` in an `epi_workflow` as well as
	`adjust_epi_recipe()` to alter the arguments to a particular step in an `epi_recipe` or `epi_workflow` by the step number or name.
	For a model, one may `add_model()`, `update_model()`, or `remove_model()` in an `epi_workflow`.
	For post-processing, where the goal is to update a frosting object or a layer in it, we have `add_frosting()`, `remove_frosting()`, and `update_frosting()` to alter the entire `frosting` object in an `epi_workflow` as
	well as `adjust_frosting()` to alter the arguments to a particular layer in a `frosting` or `epi_workflow` by
	its number or name.
	A summary of the function uses by processing step is shown by the following table:

[dajmcdon]

I prefer package names to go in curly braces. (Good use of paren on the function names here.)

Suggested change

	The `add_epi_recipe` and `remove_epi_recipe` functions offload to the `workflows` versions of the functions (`workflows::add_recipe()` and `workflows::remove_recipe()`) as much as possible. The main reason for using the `epipredict` version is so that we ensure that we do not lose the `epi_workflow` class.
	The `add_epi_recipe()` and `remove_epi_recipe()` functions offload to the `{workflows}` versions of the
	functions as much as possible. The main reason for using the `{epipredict}` version is so that we ensure
	that we retain the `epi_workflow` class.

[dajmcdon]

Suggested change

	workflows::remove_recipe(wf) %>% class() # class after removing recipe using workflows function
	workflows::remove_recipe(wf) %>% class() # class after removing recipe using workflows function

[dajmcdon]

Suggested change

	workflows::extract_preprocessor(wf) # step_epi_ahead is the third step in r2
	tidy(workflows::extract_preprocessor(wf)) # tidy tibble summary of r2
	extract_preprocessor(wf) # step_epi_ahead is the third step in r2
	tidy(extract_preprocessor(wf)) # tidy tibble summary of r2

[dajmcdon]

Suggested change

	workflows::extract_preprocessor(wf)
	extract_preprocessor(wf)

[dajmcdon]

Suggested change

	workflows::extract_preprocessor(wf)
	extract_preprocessor(wf)

[rachlobay]

I think I'm going to keep the workflows:: for now because it's a quick and clear way to indicate what functions I used are from that package & I think it's good to lay that out somewhere (because otherwise it can be hard to tell for a beginner which functions are from that package and which are from ours - because it's not exceedingly common).