U.S. SMS address needs to start with +1, not 001

[CF20852]

In https://github-wiki-see.page/m/botletics/SIM7000-LTE-Shield/wiki/SMS-Messages, we are instructed to set the country code for U.S. addressees to "001" when using the 's' command. That doesn't work. "+1" does work, at least with the Hologram SIM.

Also, when using the Arduiono Serial Monitor, you have to make sure to set the line ending to New Line or both CR and NL. The Botletics_modem::readline() function looks for the NL character (0x0A) as the line terminator. This should be explicitly mentioned in the user docs.