Add Truncate All Rows as a postgres til.

postgres/truncate-all-rows.md

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+# Truncate All Rows
+
+Given a postgres database, if you want to delete all rows in a table, you
+can use the `DELETE` query without any conditions.
+
+```
+> delete from pokemons;
+DELETE 151
+```
+
+Though `DELETE` can do the job, if you really are deleting all rows to clear
+out a table, you are better off using `TRUNCATE`. A `TRUNCATE` query will be
+faster than a `DELETE` query because it will just delete the rows without
+scanning them as it goes.
+
+```
+> truncate pokemons;
+TRUNCATE TABLE
+```
+
+[source](http://www.postgresql.org/docs/8.2/static/sql-truncate.html)