Add some developer-facing documentation (#69)

Whenever I touch this project I don't remember how to perform the most
common tasks, I figured let's document them.

README.md

@@ -4,6 +4,8 @@ This repo is a friendly fork of the excellent https://github.com/ferdikoomen/ope
 generator to better fit our exact use case. Some of these changes we'll try to get merged into the upstream, but some are more of a specific
 use case for us, hence the need for a fork. This code is used by https://github.com/lune-climate/lune-ts to generate the base models/services.
 
+We have some [Developer documentation](docs/dev.md).
+
 # Release process
 
 Changes made to the library will only be picked up by `lune-ts` once a new version is released to npm.
@@ -78,6 +80,8 @@ $ openapi --help
 
 # Documentation
 
+For end-users:
+
 -   [Basic usage](docs/basic-usage.md)
 -   [OpenAPI object](docs/openapi-object.md)
 -   [Client instances](docs/client-instances.md) `--name`
@@ -89,6 +93,10 @@ $ openapi --help
 -   [Authorization](docs/authorization.md)
 -   [External references](docs/external-references.md)
 
+For developers:
+
+-   [Developer documentation](docs/dev.md)
+
 # Support
 
 -   [Babel support](docs/babel-support.md)

docs/dev.md

@@ -0,0 +1,29 @@
+# Developer documentation
+
+This document is for the developers of this project, not for the users.
+
+## Common commands
+
+Install the dependencies:
+
+```
+npm install
+```
+
+Build the project (doesn't run the tests):
+
+```
+npm run build
+```
+
+Run the tests (we have to build in order for the current code to be used):
+
+```
+npm run build && npm run test
+```
+
+Update the test snapshots (we have to build in order for the current code to be used):
+
+```
+npm run build && npm run test -- -u
+```