Update usage.rst to include self-referencing notice

Updates the bidirectional linking documentation for records/tables to note that the intended use for the field is not for self-referencing.

docs/usage.rst

@@ -155,6 +155,8 @@ To add a link to a related record object, you can use the ``add_related_recid``
 
 In the last example, we are adding a link to the submission with the record ID value of ``3``.
 
+**Please note:** This field should not be used for self-referencing, the IDs inserted should be for OTHER related records.
+
 The documentation for this feature can be found here: `Linking records`_.
 
 .. _`Linking records`: https://hepdata-submission.readthedocs.io/en/latest/bidirectional.html#linking-records
@@ -312,6 +314,8 @@ To add a link to a related table object, you can use the ``add_related_doi`` fun
 
 In the second example, we are adding a link to the table with a DOI value of `10.17182/hepdata.12882.v1/t2 <https://doi.org/10.17182/hepdata.12882.v1/t2>`_.
 
+**Please note:** This field should not be used for self-referencing, the DOIs inserted should be for OTHER related tables.
+
 The documentation for this feature can be found here: `Linking tables`_.
 
 .. _`Linking tables`: https://hepdata-submission.readthedocs.io/en/latest/bidirectional.html#linking-tables