Add clarification for getting started with Influx CLI page

User has installed InfluxDB but is having trouble getting started with Influx CLI.

Add the following to the top of this doc:

The influx CLI is packaged separately from InfluxDB, so installing InfluxDB doesn't automatically install the influx CLI. If you haven't aleady, [download and install the influx CLI](https://docs.influxdata.com/influxdb/v2.3/install/#download-and-install-the-influx-cli).

New user feedback!

Page: https://docs.influxdata.com/influxdb/v2.3/reference/cli/
Feedback: All of the reference documents I am looking at for integrating JMeter and InfluxDB show running the influxdb as a shell.  The version 2.3 does not seem to have this!  Also the samples I see do not seem to show any authorization tokens, but it looks like the version I installed requires them.  I am about to give up. I need this to  "just work" - not be a major undertaking to get JMeter data into influx

Open the InfluxDB v2.3 CLI reference page linked in the issue and review the current introduction. Add the supplied clarification at the top, preserving its download link, then preview the rendered page to confirm the wording and link display correctly.

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