Typos a/an (#13819)

bundles/org.openhab.persistence.rrd4j/README.md

@@ -75,7 +75,7 @@ It must be an alphanumeric string.
 Defines the type of data to be stored.
 It must be one of the following string values:
 
-- **COUNTER** represents a ever-incrementing value (historically this was used for packet counters or traffic counters on network interfaces, a typical home-automation application would be your electricity meter). If you store the values of this counter in a simple database and make a chart of that, you'll most likely see a nearly flat line, because the increments per time are small compared to the absolute value (e.g. your electricity meter reads 60567 kWh, and you add 0.5 kWh per hour, than your chart over the whole day will show 60567 at the start and 60579 at the end of your chart. That is nearly invisible. RRD4J helps you out and will display the difference from one stored value to the other (depending on the selected size). Please note that the persistence extensions will return difference instead of the actual values if you use this type; this especially leads to wrong values if you try to restoreOnStartup!
+- **COUNTER** represents an ever-incrementing value (historically this was used for packet counters or traffic counters on network interfaces, a typical home-automation application would be your electricity meter). If you store the values of this counter in a simple database and make a chart of that, you'll most likely see a nearly flat line, because the increments per time are small compared to the absolute value (e.g. your electricity meter reads 60567 kWh, and you add 0.5 kWh per hour, than your chart over the whole day will show 60567 at the start and 60579 at the end of your chart. That is nearly invisible. RRD4J helps you out and will display the difference from one stored value to the other (depending on the selected size). Please note that the persistence extensions will return difference instead of the actual values if you use this type; this especially leads to wrong values if you try to restoreOnStartup!
 - **GAUGE** represents the reading of e.g. a temperature sensor. You'll see only small deviation over the day and your values will be within a small range, clearly visible within a chart.
 - **ABSOLUTE** is like a counter, but RRD4J assumes that the counter is reset when the value is read. So these are basically the delta values between the reads.
 - **DERIVE** is like a counter, but it can also decrease and therefore have a negative delta.