chore(gatsby-source-graphql): docs on how to use apollo links

[vladar]

Description

Add a section to the gatsby-source-graphql plugin docs about Apollo links and how to compose them.

Related Issues

See #28680

[meganesu]

Left some suggestions. Feel free to reach out with questions or other ideas!

[meganesu]

Could you add something about what the parameters are for the createLink option?

[vladar]

I've added a comment in the example. We also have some examples of this option at the beginning of the readme.

[meganesu]

This intro paragraph could use a bit more context, to help people figure out whether or not this option is something they need.

Possible structure: (Feel free to correct the wording, since I don't totally know how this plugin works)

(You might not actually need the headings, I just added them to highlight the different chunks of information)

---

Introduction

[Sentence describing the problem (e.g., "Sometimes network requests fail, but that doesn't mean you want your query to fail.")] You can use the plugin's createLink option to add an Apollo Link to your GraphQL operation.

(For more explanation of how Apollo Links work, check out this Medium article: Productionalizing Apollo Links.)

Types of Links

You can create different types of links, depending on the functionality you're trying to achieve:

• apollo-link-retry for retrying requests that time out
• [some other lib] for error handling
• [some other lib] for [whatever other thing they're trying to do]

// goal of the list above is to point them toward the right lib if they're trying to do this for the first time

Parameters

To use the createLink option in your gatsby-config.js, pass it [explanation of the parameters].

Example

Here's an example of using the HTTP link with retries (using apollo-link-retry):

[code snippet]

[vladar]

Thank you, this is so much better 👍

[meganesu]

Looks great! ✨👏