Add command to print log time range

Just a simple addition of a command that
grabs the first/last line and extracts time into
a nice range-like output

doc/administration/logs.md

@@ -14,10 +14,12 @@ Find more about them [in Audit Events documentation](audit_events.md).
 System log files are typically plain text in a standard log file format.
 This guide talks about how to read and use these system log files.
 
-Read more about how to
-[customize logging on Omnibus GitLab installations](https://docs.gitlab.com/omnibus/settings/logs.html)
+Read more about the log system and using the logs:
+
+- [Customize logging on Omnibus GitLab installations](https://docs.gitlab.com/omnibus/settings/logs.html)
 including adjusting log retention, log forwarding,
 switching logs from JSON to plain text logging, and more.
+- [How to parse and analyze JSON logs](troubleshooting/log_parsing.md).
 
 ## `production_json.log`
 

doc/administration/troubleshooting/log_parsing.md

@@ -41,6 +41,20 @@ jq -cR 'fromjson?' file.json | jq <COMMAND>
 By default `jq` will error out when it encounters a line that is not valid JSON.
 This skips over all invalid lines and parses the rest.
 
+#### Print a JSON log's time range
+
+```shell
+cat log.json | (head -1; tail -1) | jq '.time'
+```
+
+Use `zcat` if the file has been rotated and compressed:
+
+```shell
+zcat @400000006026b71d1a7af804.s | (head -1; tail -1) | jq '.time'
+
+zcat some_json.log.25.gz | (head -1; tail -1) | jq '.time'
+```
+
 ### Parsing `production_json.log` and `api_json.log`
 
 #### Find all requests with a 5XX status code