docs(tut): Add cross ref to chapter 6

[VorpalBlade]

This helps when users try to use the docs as a reference to solve their issue at hand (as opposed to reading in order and remembering everything).

Related to discussion #544

[coveralls]

Pull Request Test Coverage Report for Build 9652374114

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.4%) to 42.044%

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Files with Coverage Reduction	New Missed Lines	%
src/token/mod.rs	1	75.0%
src/macros/seq.rs	2	85.71%

Totals
Change from base Build 9407425121:	0.4%
Covered Lines:	1308
Relevant Lines:	3111

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💛 - Coveralls

[VorpalBlade]

I don't think that "coveralls" report is correct. I haven't changed any of the files it claims have new missed lines...

[epage]

I feel this doesn't quite serve the intended role.

• Everything up to this point was already relying on this in this chapter
• If we had this, I feel like it should call out the mechanism whereby this is done or else it feels like its pointing back to nothing
• I believe our callbacks like this are usually done when we reference much earlier chapters. What some chapters do for this type of thing is, at the very type, have a transition statement. For example, we could have something like "With Parser::parse converting PResult into Result for use in our application, let's see how we can polish the quality of the reported error message". Note that that example statement is meant only to serve as an example and I created it without much deep thought.

[VorpalBlade]

Change apparently not wanted at all (seemed like an outright reject rather than suggestions for how to improve the PR) and I don't have time to work on this.

[epage]

To be clear, I gave a first-order approximation of how this could be reworked

For example, we could have something like
"With Parser::parse converting PResult into Result for use in our application, let's see how we can polish the quality of the reported error message".