Add tech research

research.md

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+## Proposed Tech stack
+- NodeJS
+- Express
+- Postgresql
+- Luxon
+
+## How to deal with date and time in PostgreSQL?
+- use `datetime` datatype without timezone (datetime with timezone is using offset, which doesn't work well with DST)
+- store datetime in UTC
+- add timezone information separately, use `Full time zone name` (human friendly)
+- use `ISO 8601` format, which is human friendly to read and supported by every library
+
+
+See:
+- https://www.moesif.com/blog/technical/timestamp/manage-datetime-timestamp-timezones-in-api/
+- https://www.postgresql.org/docs/current/datatype-datetime.html