docs: add darkmode image to readme

[Weetbix]

This adds darkmode support to the logo in the readme:

[github-actions]

Overall readability score: 34.76 (🟢 +0)

File	Readability
README.md	67.63 (🟢 +0)

View detailed metrics 👀

🟢 - Shows an increase in readability
🔴 - Shows a decrease in readability

File	Readability	FRE	GF	ARI	CLI	DCRS
README.md	67.63	55.03	9.2	10.7	10.55	6.83
	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0

Averages:

	Readability	FRE	GF	ARI	CLI	DCRS
Average	34.76	18.55	14.91	14.45	14.46	8.72
	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0

View metric targets

Metric	Range	Ideal score
Flesch Reading Ease	100 (very easy read) to 0 (extremely difficult read)	60
Gunning Fog	6 (very easy read) to 17 (extremely difficult read)	8 or less
Auto. Read. Index	6 (very easy read) to 14 (extremely difficult read)	8 or less
Coleman Liau Index	6 (very easy read) to 17 (extremely difficult read)	8 or less
Dale-Chall Readability	4.9 (very easy read) to 9.9 (extremely difficult read)	6.9 or less

[noon-dawg]

🕶️