x/website: Managing Go installations is out of date

[luantak]

With go 1.17 go get doesn't install binaries anymore (see https://golang.org/doc/go-get-install-deprecation)

The documentation at https://golang.org/doc/manage-install is out of date it should use the new go install syntax:
go install golang.org/dl/go1.10.7@latest

instead of the current go get golang.org/dl/go1.10.7 which errors:

go get: installing executables with 'go get' in module mode is deprecated.
        Use 'go install pkg@version' instead.
        For more information, see https://golang.org/doc/go-get-install-deprecation
        or run 'go help get' or 'go help install'.

[fzipp]

Other instances of deprecated go get usage on the website: #43684 (comment)

[gopherbot]

Change https://golang.org/cl/347211 mentions this issue: _content/doc: update multiple go install instructions