Clarify wording in metrics documentation

doc/administration/monitoring/prometheus/gitlab_metrics.md

@@ -62,8 +62,8 @@ Some basic Ruby runtime metrics are available:
 | ruby_sampler_duration_seconds_total    | Counter   | 11.1  | Time spent collecting stats |
 | ruby_process_cpu_seconds_total         | Gauge     | 11.11 | Total amount of CPU time per process |
 | ruby_process_max_fds                   | Gauge     | 11.11 | Maximum number of open file descriptors per process |
-| ruby_process_resident_memory_bytes     | Gauge     | 11.11 | Memory usage by process |
-| ruby_process_start_time_seconds        | Gauge     | 11.11 | The time the process started after system boot in seconds |
+| ruby_process_resident_memory_bytes     | Gauge     | 11.11 | Memory usage by process, measured in bytes |
+| ruby_process_start_time_seconds        | Gauge     | 11.11 | The elapsed time between system boot and the process started, measured in seconds |
 
 [GC.stat]: https://ruby-doc.org/core-2.3.0/GC.html#method-c-stat