Add missing migrationscript messages

migrations/versions/5fe6a6c7870c_.py

-"""empty message
+"""Add corpus follower associations table
 
 Revision ID: 5fe6a6c7870c
 Revises: 5b2a6e590166

migrations/versions/f2656133df2f_.py

-"""empty message
+"""Rename shared columns to is_public and add description column to corpus_files table
 
 Revision ID: f2656133df2f
 Revises: 31b9c0259e6b