Fabric ca getting started documentation is out of date

In the documentation for getting started the following is defined
```
Go 1.10+ installation
GOPATH environment variable is set correctly
libtool and libtdhl-dev packages are installed
```
However Go 1.16 is now required and GOPATH doesn't need to be set

In the install section it says to use
```
go get -u github.com/hyperledger/fabric-ca/cmd/...
```
This will fail due to a breaking api change in go-kit (see https://stackoverflow.com/questions/69565838/i-encountered-an-error-while-installing-fabric-ca-with-the-go-get-command)

One solution is to remove the `-u` option but I don't know if that would download, build and install a version using the exact same dependencies that the official builds use (anyone able to confirm ?)

The alternative would be to reference the official build packages instead ? (suggestions please)

Also the following text still refers to the master branch
```
Note: If you have already cloned the fabric-ca repository, make sure you are on the master branch before running the ‘go get’ command above. Otherwise, you might see the following error:
```