Adds info about plangenerator to README.

README.md

@@ -85,6 +85,18 @@ Prior to running the tests locally, ensure you have the following environmental
 - `JUJU_PASSWORD`
 - `JUJU_CA_CERT`
 
+### Writing Acceptance Tests
+
+Acceptance tests usually require Terraform plans to be included to the various steps of the test. 
+This plans can be generated with help of `testing/plangenerator` package. You may use `GetStringFromTemplateWithData`
+function to generate a plan from a template. This function will replace the placeholders in the template with the data. 
+
+The example can be found in the comments to `GetStringFromTemplateWithData` function.
+
+### Testing
+
+```shell
+
 For example, here they are set using the currently active controller:
 
 ```shell