docs: update readme with examples

.github/CONTRIBUTING.md

@@ -0,0 +1,24 @@
+# Contributing
+
+We love contributions! You are welcome to open a pull request, but it's a good idea to
+open an issue and discuss your idea with us first.
+
+Once you are ready to open a PR, please keep the following guidelines in mind:
+
+1. Code should be `go fmt` compliant.
+2. Types, structs and funcs should be documented.
+3. Tests and linters pass.
+
+## Getting set up
+
+`xelon-sdk-go` uses go modules. Just fork this repo, clone your fork and off you go!
+Run `make help` to see all available make commands.
+
+
+## Running tests and lint
+
+When working on code in this repository, tests and linters can be run via:
+
+```shell
+make lint test
+```

README.md

@@ -5,3 +5,67 @@
 [![GoDoc](https://img.shields.io/badge/pkg.go.dev-doc-blue)](http://pkg.go.dev/github.com/Xelon-AG/xelon-sdk-go)
 
 xelon-sdk-go is the official Xelon SDK for the Go programming language.
+
+## Installation
+
+```sh
+# X.Y.Z is the version you need
+go get github.com/Xelon-AG/xelon-sdk-go@vX.Y.Z
+
+
+# for non Go modules usage or latest version
+go get github.com/Xelon-AG/xelon-sdk-go
+```
+
+## Usage
+
+```go
+import "github.com/Xelon-AG/xelon-sdk-go"
+```
+
+Create a new Xelon client, then use the exposed services to access
+different parts of the Xelon API.
+
+### Authentication
+
+Currently, Bearer token is the only method of authenticating with the API.
+You can learn how to obtain it [here](https://www.xelon.ch/docs/xelon-api-101#authorize-youself).
+Then use your token to create a new client:
+
+```go
+client := client := xelon.NewClient("my-secret-token")
+```
+
+If you want to specify more parameters by client initialization, use
+`With...` methods and pass via option pattern:
+
+```go
+var opts []xelon.ClientOption
+opts = append(opts, xelon.WithBaseURL(baseURL))
+opts = append(opts, xelon.WithClientID(clientID))
+opts = append(opts, xelon.WithUserAgent(userAgent))
+
+client := client := xelon.NewClient("my-secret-token", opts...)
+```
+
+### Examples
+
+List all ssh keys for the user.
+
+```go
+func main() {
+  client := xelon.NewClient("my-secret-token")
+
+  // list all ssh keys for the authenticated user
+  ctx := context.Background()
+  sshKeys, _, err := client.SSHKeys.List(ctx)
+}
+```
+
+## Contributing
+
+We love pull requests! Please see the [contribution guidelines](.github/CONTRIBUTING.md).
+
+## License
+
+This SDK is distributed under the Apache-2.0 license, see [LICENSE](LICENSE) for more information.