Add memory management section to simple vector store

[OlegIvaniv]

This PR adds a section SImple Memory Vector store explaining the mechanics of memory management that are going to be introduced here: https://github.com/n8n-io/n8n/pull/13986

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[github-actions[bot]]

Overall readability score: 44.74 (🟢 +0)

File	Readability
n8n-nodes-langchain.vectorstoreinmemory.md	56.55 (🔴 -2.05)

View detailed metrics

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

File	Readability	FRE	GF	ARI	CLI	DCRS
n8n-nodes-langchain.vectorstoreinmemory.md	56.55	45.25	10.51	13.5	12.76	6.84
	🔴 -2.05	🟢 +1.01	🔴 -0.52	🟢 +0.1	🔴 -0.11	🔴 -0.41

Averages:

	Readability	FRE	GF	ARI	CLI	DCRS
Average	44.74	36.09	11.54	14.53	14.22	8.39
	🟢 +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

[github-actions[bot]]

Summary

Status	Count
🔍 Total	12
✅ Successful	3
⏳ Timeouts	0
🔀 Redirected	0
👻 Excluded	9
❓ Unknown	0
🚫 Errors	0
Full Github Actions output