Better document how to install the cli

[omerlh]

There is a link to docker hub, but might be easier for readers to add an example commands like

 docker run -v $(pwd):/service -it effx/effx-cli sync -f /service/service.yaml -k <>
2020/06/25 05:19:26 file_path /service/service.yaml is invalid

Also, I tried to install it with go get and it failed:

go get github.com/effxhq/effx-cli
# cd .; git clone -- https://github.com/effxhq/effx-api /Users/omerlh/go/src/github.com/effxhq/effx-api
Cloning into '/Users/omerlh/go/src/github.com/effxhq/effx-api'...
ERROR: Repository not found.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
package github.com/effxhq/effx-api/generated/go: exit status 128

Will be nice if this will be supported, or even a brew formula