document that honor timestamps should be enabled

[uhthomas]

The exporter can limit how often it scrapes the Tesla API to avoid rate limiting. It does this by caching metrics and only updating them after the specified internal. It also does this lazily, when a request is made to the exporter. The exporter correctly exports metrics with timestamps to indicate that they may be stale, and to accurately represent when the metrics were scraped. Some projects, like VictoriaMetrics, do not honor timestamps by default.

https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4697

https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config

# honor_timestamps controls whether Prometheus respects the timestamps present
# in scraped data.
#
# If honor_timestamps is set to "true", the timestamps of the metrics exposed
# by the target will be used.
#
# If honor_timestamps is set to "false", the timestamps of the metrics exposed
# by the target will be ignored.
[ honor_timestamps: [<boolean>](https://prometheus.io/docs/prometheus/latest/configuration/configuration/#boolean) | default = true ]