update appium/README.md with how to install/use/configure appium inspector

[tomholub]

@Kharchevskyi later please add to appium/README.md how to install and use the above tool and how to configure it so that others can also do it. I'm filing a separate issue.

Originally posted by @tomholub in #1127 (comment)

[Kharchevskyi]

@tomholub please check https://github.com/FlowCrypt/flowcrypt-ios/blob/master/appium/README.md
is it ok? or need to add smth more?

[tomholub]

yes this helps