Change after to next in badge rule

[hstsethi]

I believe it is more clear. After implies beside.

I tried putting it after but it wouldn't stop throwing errors until the badge was placed next to it.

The guidelines also read:

Should be placed on the right side of the readme heading.

[hstsethi]

I have now changed test rules to accommodate for new error message, but this pull request will fail the checks until the updated rules are merged.

I can create another pull request if maintainers feel like the new error message is better.