Mention other device integrations in "Connect a device" and Get started

In the "Connect a device" dialog in the UI (and our Get started), Yocto (or other boards than RPi) is not mentioned at all. This is by design, in order to simplify the first steps (single path, optimized user journey).

However, the key problem is that this is perceived by some users that RPi is the only thing Mender supports. To alleviate this, we should mention that you can connect virtually any kind of device and Linux OS, but we recommend that you go through the onboarding first.

Acceptance criteria

• There is a note in "Connect a device" UI about integrating other types of devices and Linux OSes. It can link to https://docs.mender.io/system-updates-debian-family, https://docs.mender.io/system-updates-yocto-project and/or https://hub.mender.io/c/board-integrations, depending on the exact text.

• The Get started -> Preparation also includes the same note.