update installation instructions with method to provide OSF credentials (#186)

* update installation instructions with method to provide OSF credentials

* clarified OSF credential update

Author: B-Sevchik

docs/source/installation.rst

@@ -76,8 +76,8 @@ How to install ``datalad-osf``::
     # Install datalad-osf:
     pip install datalad-osf
 
-    # Provide your OSF credentials (token) - this step is very important!
-    datalad osf-credentials
+    # Provide your OSF credentials  - this step is very important!
+    datalad osf-credentials --method userpassword
 
 
 Installation reference