Add yaml for Krew installation

[int128]

This adds the yaml for Krew installation. See #34.

This has been tested on local but not tested with actual GitHub Releases.

% kubectl krew install --manifest dist/gh/oidc-login.yaml --archive dist/gh/kubelogin_darwin_amd64.zip
Installing plugin: oidc-login
CAVEATS:
\
 |  You need to setup the following components:
 |    * OIDC provider
 |    * Kubernetes API server
 |    * Role for your group or user
 |    * kubectl authentication
 |
 |  See https://github.com/int128/kubelogin for more.
/
Installed plugin: oidc-login

% kubectl oidc-login -h

% kubectl krew remove oidc-login

[int128]

🎉 Tested with GitHub Releases:

% curl -LO https://github.com/int128/kubelogin/releases/download/v1.9.0/oidc-login.yaml

% kubectl krew install --manifest oidc-login.yaml
kubectl completion zsh...
Installing plugin: oidc-login
CAVEATS:
\
 |  You need to setup the following components:
 |    * OIDC provider
 |    * Kubernetes API server
 |    * Role for your group or user
 |    * kubectl authentication
 |
 |  See https://github.com/int128/kubelogin for more.
/
Installed plugin: oidc-login

% kubectl oidc-login -h
2019/04/05 10:45:56 Usage:
  kubectl-oidc_login [OPTIONS]

Version v1.9.0