Mention to adjust the espflash baud-rate #232
Description
In https://docs.espressif.com/projects/rust/book/getting-started/tooling/espflash.html we could hint users to adjust the baud-rate via the env var
e.g. I use ESPFLASH_BAUD=2000000 - but at least 921600 should work for almost everyone
Might make things a bit smoother for most users