Update cheatsheets

tldr/postgres

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# postgres
+
+> Run the PostgreSQL database server.
+> More information: <https://www.postgresql.org/docs/current/app-postgres.html>.
+
+- Start the server on a specific port (defaults to 5432):
+
+`postgres -p {{5433}}`
+
+- Set a runtime parameter (short form):
+
+`postgres -c {{shared_buffers=128MB}}`
+
+- Set a runtime parameter (long form):
+
+`postgres --{{shared-buffers}}={{128MB}}`
+
+- Start in single-user mode for a specific database (defaults to the user name):
+
+`postgres --single -D {{path/to/datadir}} {{my_database}}`