docs: add doc for gen apis and mocks

Signed-off-by: He Weiwei <hweiwei@vmware.com>

CONTRIBUTING.md

@@ -77,6 +77,20 @@ The folder graph below shows the structure of the source code folder `harbor/src
 │   ├── secret
 │   ├── security
 │   └── utils
+├── controller          # Source code for the controllers used by the API handlers.
+│   ├── artifact
+│   ├── blob
+│   ├── event
+│   ├── icon
+│   ├── p2p
+│   ├── project
+│   ├── proxy
+│   ├── quota
+│   ├── repository
+│   ├── scan
+│   ├── scanner
+│   ├── tag
+│   ├── task
 ├── core                # Source code for the main busines logic. Contains rest apis and all service infomation.
 │   ├── api
 │   ├── auth
@@ -112,6 +126,12 @@ The folder graph below shows the structure of the source code folder `harbor/src
 │   └── src             # General web page UI code of Harbor
 ├── registryctl         # Source code contains the main logic to handle registry.
 ├── replication         # Source code contains the main logic of replication.
+├── server              # Source code for the APIs.
+│   ├── handler
+│   ├── middleware
+│   ├── registry
+│   ├── router
+│   ├── v2.0
 ├── testing             # Some utilities to handle testing.
 └── vendor              # Go code dependencies
     ├── github.com
@@ -142,7 +162,7 @@ Harbor backend is written in [Go](http://golang.org/). If you don't have a Harbo
 
 Ensure your GOPATH and PATH have been configured in accordance with the Go environment instructions.
 
-**Dependency Management:** Harbor uses [dep](https://github.com/golang/dep) for dependency management of go code.  The official maintainers will take the responsibility for managing the code in `vendor` directory.  Please don't try to submit a PR to update the dependency code, open an issue instead.  If your PR requires a change in the vendor code please make sure you discuss it with the maintainers in advance.
+**Dependency Management:** Harbor uses [Go modules](https://github.com/golang/go/wiki/Modules) for dependency management of go code.  The official maintainers will take the responsibility for managing the code in `vendor` directory.  Please don't try to submit a PR to update the dependency code, open an issue instead.  If your PR requires a change in the vendor code please make sure you discuss it with the maintainers in advance.
 
 #### Web
 
@@ -250,6 +270,10 @@ npm run test
 
 To build the code, please refer to [build](https://goharbor.io/docs/2.0.0/build-customize-contribute/compile-guide/) guideline.
 
+**Note**: from v2.0, Harbor uses [go-swagger](https://github.com/go-swagger/go-swagger) to generate API server from Swagger 2.0 (aka [OpenAPI 2.0](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md)). To add or change the APIs, first update the `api/v2.0/swagger.yaml` file, then run `make gen_apis` to generate the API server, finally, implement or update the API handlers in `src/server/v2.0/handler` package.
+
+As now Harbor uses `controller/manager/dao` programming model, we suggest to use [testify mock](github.com/stretchr/testify/mock) to test `controller` and `manager`. Harbor integrates [mockery](https://github.com/vektra/mockery) to generate mocks for golang interfaces using the testify mock package. To generate mocks for the interface, first add `//go:generate mockery xxx` comment with mockery command in the subpackages of `src/testing`, then run `make gen_mocks` to generate mocks.
+
 ###  Keep sync with upstream