Add docs for Postgres Chat Memory

[OlegIvaniv]

n8n-io/n8n#10071

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[github-actions]

Overall readability score: 42.29 (🔴 -0.02)

File	Readability
understand-memory.md	51.39 (🟢 +0)
langchain-n8n.md	53.7 (🟢 +0)
n8n-nodes-langchain.memorypostgreschat.md	13.97 (-)
postgres.md	76.04 (🟢 +0)

View detailed metrics

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

File	Readability	FRE	GF	ARI	CLI	DCRS
understand-memory.md	51.39	32.19	9.23	13	14.09	8.1
	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0
langchain-n8n.md	53.7	42.27	8.33	13.8	15.07	7.59
	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0
n8n-nodes-langchain.memorypostgreschat.md	13.97	7.25	14.57	22	19	9.39
	-	-	-	-	-	-
postgres.md	76.04	52.56	6.2	9.3	11.05	6.1
	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0

Averages:

	Readability	FRE	GF	ARI	CLI	DCRS
Average	42.29	34.22	11.79	15.02	14.44	8.6
	🔴 -0.02	🔴 -0.02	🟢 +0	🔴 -0.01	🟢 +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