Add example to rfc3339's docs

[Shadlock0133]

No description provided.

[codecov]

Codecov Report

Merging #391 (b8c5b5d) into main (be29bb3) will not change coverage.
The diff coverage is n/a.

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  Coverage   99.69%   99.69%           
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  Files          52       52           
  Lines        5574     5574           
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  Hits         5557     5557           
  Misses         17       17           

Impacted Files	Coverage Δ
src/format_description/mod.rs	100.00% <ø> (ø)

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[jhpratt]

If we're going to add an example, why not have it be actual code showing how it's used?

[Shadlock0133]

Rfc3339 is a struct representing a format description, so I would expect an example of the format, and maybe a format description string?
I think code examples makes sense on parse/format functions, which already have them. But maybe Rfc3339 could have links, like:

/// The format described in [RFC 3339](https://tools.ietf.org/html/rfc3339#section-5.6).
///
/// Format description: "[year]-[month]-[day]T[hour]:[minute]:[second].[subsecond]Z"
///
/// Example: 1985-04-12T23:20:50.52Z
///
/// Can be used with `parse` and `format` functions of [`Time`], [`Date`], ...
pub struct Rfc3339;

[jhpratt]

Perhaps having some sort of indication that it can be passed to those methods is what I was envisioning. One thing we don't want, though, is the "[year]-[month]-[day]T[hour]:[minute]:[second].[subsecond]Z" comment — it's not accurate as there are nuances that make it different.

[jhpratt]

LGTM. Thanks.