message: Added documentation for history timestamps
diff: @@ -102,3 +102,8 @@ Defaults to **$HOME/.local/share/ion/history**
  Specifies how many commands should be saved in `HISTFILE` at most.
  Ideally, this should have the same value as `HISTORY_SIZE`.
  Defaults to **100000**.
  +
  +### HISTORY_TIMESTAMP
  +Specifies whether a corresponding timestamp should be recorded along with each command.
  +The timestamp is indicated with a `#` and is unformatted as the seconds since the unix epoch.
  +This feature is disabled by default and can be enabled by executing the following command: `let HISTORY_TIMESTAMP = 1`.
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