Add notes about problems regenerating the tables

sql/README.md

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+# SQL
+
+The SQL files were generated using pgAdmin on Windows.
+
+## Problems
+
+If you are using a macOS to regenerate the database, be aware:
+
+For create-full-stack-db.sql, remove the following lines if you get a complaint about them:
+
+```
+LC_COLLATE = 'English_United States.1252'
+LC_CTYPE = 'English_United States.1252'
+```
+
+For create-users.sql, it will complain about the sequence. Replace the definition of id with:
+
+```
+id SERIAL NOT NULL,
+```
+
+There is no need to run the create-users-seq.sql file.
+
+Similarly, do the same for create-message.sql.