Update README.md

Author: nick-iles

README.md

@@ -14,7 +14,9 @@ To add the library to your project:
 
 Full plugin configuration below, optional properties can be omitted.  
 
-project_id, access_key secret_key can be found from the  [asserthat configuration page](https://assertthat.atlassian.net/wiki/spaces/ABTM/pages/725385217/Configuration)
+Either use access_key/sectret_key OR token authentication:
+- project_id, access_key secret_key can be found from the  [asserthat configuration page](https://assertthat.atlassian.net/wiki/spaces/ABTM/pages/725385217/Configuration)
+- Personal Access token can be generated on [Data Center](https://confluence.atlassian.com/enterprise/using-personal-access-tokens-1026032365.html) or [Cloud](https://id.atlassian.com/manage-profile/security/api-tokens).  project_id details can be found here [asserthat configuration page](https://assertthat.atlassian.net/wiki/spaces/ABTM/pages/725385217/Configuration)
 
 ```
 from assertthat_bdd.jira_integration import JiraConnector