docs(README): add info to jira output (#329)

* docs(README): add info to jira output

Added info about using 'unknowns' field in jira output

* docs(readme): changed jira output information

added instruction for get field name from Jira UI

* chore(images): jira ui images for README.md saved in repo

README.md

@@ -309,7 +309,63 @@ Key | Description | Possible Values
 
 For Jira you can also specify custom fields that will be populated with values.
 Use the `unknowns` parameter in cfg.yaml for custom fields.
-Under the `unknowns` parameter, specify the list of fields names to provide value for.
+Under the `unknowns` parameter, specify the list of fields **names** to provide value for. Field name can contains spaces.
+
+Possible options for getting the field name:
+
+<details> <summary> Get field name from Jira UI </summary>
+
+1. Move to your jira.
+2. Navigate to **Settings**(![cog](https://user-images.githubusercontent.com/91113035/159643662-b7a21717-58f0-4a5e-87a0-0d840046e215.png)) > **Issues** > **Custom fields** under the Fields section:
+![Custom_fields](docs/img/jira-custom_fields.png)
+3. Click on the required field.
+
+![Field_information](docs/img/jira-field_information.png)
+
+4. Get value from **Name** field.
+
+
+</details>
+
+<details> <summary> Get field name from Jira REST API </summary>
+
+
+1. Get all Jira fields [according to instructions](https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-issue-fields/#api-rest-api-3-field-get) 
+2. Find needed field:
+
+  ```
+  ...
+      "id": "customfield_10014",
+      "key": "customfield_10014",
+      "name": "Epic Link",
+      "untranslatedName": "Epic Link",
+      "custom": true,
+      "orderable": true,
+      "navigable": true,
+      "searchable": true,
+      "clauseNames": [
+        "cf[10014]",
+        "Epic Link"
+      ],
+      "schema": {
+        "type": "any",
+        "custom": "com.pyxis.greenhopper.jira:gh-epic-link",
+        "customId": 10014
+      }
+    },
+  ...
+  ```
+3. Get value from **Name** field.
+
+</details>
+
+  Example of using the `unknowns` parameter in the cfg.yaml file:
+
+```yaml
+unknowns:
+     Epic Link: "K8S-1"
+```
+  
 You can add "-numeric-field", "-multiple-value", "multiple-line-text-field", "-date-time-picker" and "-field-url" as suffix to the custom field name, to specify what is the field type.
 
 For example: