Add Turning Timing On as a postgres til.

postgres/turn-timing-on.md

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+# Turn Timing On
+
+When digging around your database and running queries, it is helpful to
+have an eye on the speed of those queries. This can give insight into
+where there are needs for optimizations.
+
+Turn timing on (and off) within `psql` by running `\timing`. With timing
+on, the duration of each query will be displayed in milliseconds after the
+output of the query.