Organise 'Recommended reading' links in a more useful way

[astreater]

Organising by date isn't particularly useful for people looking for content. Instead, we might want to group these links by either:

• type - official guidance, blog posts, thought pieces
• topic - GraphQL, OAuth
• source - GOV.UK, tech press, personal blogs

Categorising them in a meaningful way might get a bit rabbit-holey (what counts as a blogpost, for example) so the lightest lift improvement might be to group them by source:

• GOV.UK
• Other public sector (for example, there's a DWP Digital Blog post)
• Non-public sector

Again, since this page is likely to move to a different web presence, it might not be worth making these changes now, but posting this for posterity.