add doc tech update

docs/tech-update.md

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+---
+marp: true
+---
+# Tech Update
+---
+
+# Project Structure
+
+- ORM (less performance but secure (sql injection))
+  - entity
+  - migration (auto)
+  - subscriber (use the built-in subscribers only)
+- services
+  - router
+  - middleware
+  - services
+  - utils
+
+---
+# DB Used
+- sqlite
+  - local development
+  - testing
+- postgresql (NODE_ENV=production)
+
+## tips
+- for typeorm, change db type, db migrations will fail,
+- if so, delete migrations **before you make model changes**, and re-generate migrations
+
+---
+# Authentication
+- access token - 1h
+- refresh token - 14 days
+
+## benefits
+- do have log-out now
+- bit of safer
+
+---
+
+## Init processing
+1. login => 2 tokens
+2. get all ledgers  (let uses to pick, or cached front-end)
+3. get all resources for the selected ledger
+
+## access expired
+- will receive 401, pass refresh token to get new access token
+- heroku, closed each, 30 minutes, (500), recall in about 10~30 seconds
+
+## Logout
+- delete access token and refresh token
+
+---
+
+# Getting Started/Add new fix/feature
+> full stack is necessary
+
+- npm run ci
+- copy test.sqlite.backup and paste as database.sqlite, please do not rename
+  - npm run db:migrate  (if there are models change)
+
+## Fast to go through the projects
+- from router to service
+
+## example
+- add a validator
+
+---
+# Server/Platform and Deployment
+- Heroku PaaS
+  - postgresql
+- Docker
+  - dockerfile
+  - heroku.yml
+
+## example
+- switch to new backend
+
+---
+# Testing
+- npm run test
+  - jest
+  - jest setup
+
+## Integration services
+- github action
+- renovate -- dependencies management
+- codecov -- for code quality and coverage report
+
+---
+# Others to know
+- logger, pino
+  - fast
+  - does not show up the logging line
+
+---
+# Todo
+- validation middleware
+  - all create endpoints are required
+- get amount for accounts
+  - use amount id to filter the transactions