add explanations of provided metrics

README.md

@@ -20,3 +20,49 @@ ruleset(name="process_stats") {
   )
 }
 ```
+
+## Provided Metrics
+The following metrics provided by the rsyslog impstats module are tracked by rsyslog_exporter:
+
+### Actions
+Action objects describe what is to be done with a message, and are implemented via output modules.
+For each action object, the following metrics are provided:
+
+* processed - messages processed by this action
+* failed - number of messages this action failed to process
+* suspended - number of times this action was suspended
+* suspended_duration - amount of time this action has spent in a suspended state
+* resumed - number of times this action has resumed from a suspended state
+
+### Inputs
+Input objects describe message input sources.
+For each input object, the following metrics are provided:
+
+* submitted - messages submitted to this input
+
+### Queues
+Queues in rsyslog are used for the main message queue and for actions.  Additionally, each ruleset
+in an rsyslog configuration may optionally have its own separate main queue.  For each queue,
+the following metrics are provided:
+
+* size - messages currently in queue
+* enqueued - total messages enqueued during lifetime of queue
+* full - number of times the queue was full
+* discarded_full - number of times messages were discarded due to the queue being full
+* discarded_not_full - number of times messages discarded but queue was not full
+* max_queue_size - maximum size the queue reached during its lifetime
+
+### Resources
+Rsyslog tracks how it uses system resources and provides the following metrics:
+
+* utime - user time used in microseconds
+* stime - system time used in microseconds
+* maxrss - maximum resident set size
+* minflt - total number of minor faults
+* majflt - total number of major faults
+* inblock - number of filesystem input operations
+* oublock - number of filesystem output operations
+* nvcsw - number of voluntary context switches
+* nivcsw - number of involuntary context switches
+
+