docs: Flex manual, put emphasis on ethernet connection during first run process

[jwwojak]

Overview

A weak wifi connection can cause a Flex to reboot endlessly during the first run process. The solution is to make this very first network connection with an ethernet cable. A hardwired connection gives the robot a reliable way to download the software and firmware it needs on first run.

RTC-934

Sandbox:

• First Run > Connect to a network or computer
• First Run > Ethernet (Recommended on first run)
• First Run > Wifi section
• Settings > Network settings

Test Plan and Hands on Testing

Describe your testing of the PR. Emphasize testing not reflected in the code. Attach protocols, logs, screenshots and any other assets that support your testing.

Changelog

First run section
Revises first-run.md.

• Add a note to the H2 connect section.
• Move the H3 ethernet above the H3 wireless section. Make ethernet come first in the list.
• Modify H3 ethernet section header and section body. Emphasis on using ethernet first.
• Wifi H3 is now second. Modify the callout making it a tip with 2 bullets: ethernet first, don't use captive portals.

Settings section
Revises settings.md. Re-using cautionary text from the first run section. In a note in the "Network Settings" description.

Review requests

• Do all of these changes present the problem clearly and provide a solution with enough text and visual emphasis?

Risk assessment

• Moderate. Users are experiencing setup problems. Need to present solution clearly.