Don't print kubeconfig

Release notes:

The kubeconfig file is already written to disk, and when
people are doing live streams or recordings, they may not want
to be printing these secrets on the screen.

Clarifies the usage of the --server flags for embedded etcd.

Adds "context" to the command output for when people are
doing a merge of contexts.

Clarifies that K3s 1.19 ships with embedded etcd

Changelog for 0.9.13:

• PR #293 Don't print the kubeconfig by default by @alexellis
• PR #292 Update CLI wordings per k3s versions 1.19.1+ by @frezbo
• PR #291 upgrading from go 1.13 to 1.15 by @developer-guy

Commits
95fc8b0 Rename errors by @alexellis
539d698 Don't print the kubeconfig by default by @alexellis
d59e646 Docs update by @frezbo
111e2e1 Update CLI wordings per k3s versions 1.19.1+ by @frezbo
c716c18 upgrading from go 1.13 to 1.15 by @developer-guy
76cbed4 Update README.md by @alexellis
f4c58ef Update README.md by @alexellis
2647a58 Update README.md by @alexellis
3c2cc1b Update headings by @alexellis
bea0362 Add heading by @alexellis

Generated by Derek