Docs: Add sections for local dev of provider and together w. client (#876)

* update readme w. local dev instructions

* Update README.md

Co-authored-by: Julien Duchesne <[email protected]>

* Update README.md

Co-authored-by: Julien Duchesne <[email protected]>

---------

Co-authored-by: Julien Duchesne <[email protected]>

Author: eleijonmarck

README.md

@@ -23,6 +23,31 @@ Terraform](https://www.terraform.io/docs/extend/index.html) docs.
 Set up your local environment by installing [Go](http://www.golang.org). Also
 [Docker](https://docs.docker.com/install/) can be used for running tests.
 
+## Local Development with Frafana
+If you develop the provider and want to test locally with your grafana provider
+1. create a `.terraformrc` and paste the following
+```
+provider_installation {
+   dev_overrides {
+      "grafana/grafana" = "/path/to/your/grafana/terraform-provider" # this path is the diretory where the binary is built
+  }
+  # For all other providers, install them directly from their origin provider
+  # registries as normal. If you omit this, Terraform will _only_ use
+  # the dev_overrides block, and so no other providers will be available.
+  direct {}
+}
+```
+2. Run `go build` in this directory to get the binary, Terraform will use the binary you just built (it should print out a warning)
+
+## Testing the `grafana-api-golang-client` Together with the Terraform Provider
+As for testing the client, make a branch and open the provider PR with a `TODO:` to remove the replace operator, because the best way to test the changes you just made in the client is to integrate everything in the provider
+
+1. create a branch `api-client-branchname` with your changes
+2. modify the provider `go.mod`: 
+ - replace github.com/grafana/grafana-api-golang-client => github.com/grafana/grafana-api-golang-client <api-client-branchname>
+3. run `go mod tidy` in this directory
+4. pushing allows you to run the provider tests in CI
+
 ### Running Tests
 
 Acceptance tests require a running instance of Grafana. You can either handle