added psql commands

cheat/cheatsheets/psql

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+#psql is the PostgreSQL terminal interface. The following commands were tested on version 9.5.
+#Connection options:
+#-U username (if not specified current OS user is used).
+#-p port.
+#-h server hostname/address.
+
+#Connect to a specific database:
+psql -U postgres -h serverAddress -d dbName
+
+#Get databases on a server:
+psql -U postgres -h serverAddress --list
+
+#Execute sql query and save output to file:
+#Add -t to get only rows as result.
+psql -U postgres -d dbName -c 'select * from tableName;' -o 'fileName'
+
+Read commands from file:
+psql -f fileName
+
+#Restore databases from file:
+psql -f /fileName.backup postgres