Merge branch '27-add-developer-readme' into 'master'

Resolve "Add developer README"

Closes #27

See merge request !26

README.dev.md

+## Build targets
+
+(Set up as scripts in package.json)
+
+- `prepare`: lifecycle script (→ build)
+- `build`: should be removed (merge with prepare)
+- `test`: run jest (tests & coverage)
+- `start`: dev server, listens on TCP port 4000
+- `lint`: run eslint
+
+## Used software
+
+### Dev tools:
+
+- tsc: Typescript transpiler (to JavaScript)
+- NPM: package/build manager
+- babel-node: development nodeJS/Babel environment,
+  _not meant for production use_
+- Husky: git hooks manager
+- lint-staged: apply pre-commit hooks to changed files only ; runs:
+  - ESlint: linter (static code analyser)
+  - Prettier: code formatter
+- Jest: JS testing library tool
+- Gitlab-CI: gitlab Continuous Integration platform
+
+### Libraries:
+
+- OpenAPI (aka Swagger): language for RESTful interface description
+- Sofa: generate a REST interface from graphQL
+- Apollo: graphQL library
+- Express: web server
+- Nano: couchDB client library
+
+## Files
+
+### Build, configuration, metadata
+
+- `LICENSE`
+- `README.md` Doc: user
+- `README.dev.md` Doc: developer
+- `.git/` Config: Git
+- `.gitignore`
+- `package.json` Config: NPM: metadata, dependencies, scripts,
+  config (lint-staged, Husky)
+- `package-lock.json` Actual dependency tree (automatically updated)
+- `tsconfig.json` Config: tsc TypeScript compiler:  
+   `src \ {node_modules, **/__tests__/*} → dist/`
+- `.babelrc` Config: Babel compiler (??)
+- `.eslintrc.js` Config: ESlint
+- `.eslintignore`
+- `.prettierignore` Config: Prettier
+- `jest.config.js` Config: Jest (roots: src/ & test/ ; TS transformer)
+- `.gitlab-ci.yml` Config: continuous integration
+- `Dockerfile` Config: Docker build
+- `.dockerignore`
+
+### Code
+
+- `swagger.yml` OpenAPI Specification
+- `src/` Code
+  - `service.ts` GraphQL schema definition & resolvers
+  - `test/` Tests (Jest)
+
+### Artifacts (untracked):
+
+- `node_modules/` Dependencies,
+  created & populated by `npm install`
+- `dist/` JS files,
+  created & populated by `npm prepare` (tsc)
+- `coverage/` Tests coverage,
+  created & populated by `npm test` (jest)