deploying bundle requires README.md

[John A Meinel]

I'm trying to test out bundle deployment with Charmhub, and was able to successfully upload a bundle to the staging charmhub api. However, when I first tried to deploy it I got:

```
$ juju deploy jam-snappass-bundle3 --debug
16:32:50 INFO juju.cmd supercommand.go:56 running juju [2.9-rc11 0 101dea66b90c3d9ebf11fd5567a6b160cfb796df gc go1.16.3]
16:32:50 DEBUG juju.cmd supercommand.go:57 args: []string{"juju", "deploy", "jam-snappass-bundle3", "--debug"}
16:32:50 INFO juju.juju api.go:78 connecting to API addresses: [localhost:40511 10.152.183.101:17070]
16:32:50 DEBUG juju.api apiclient.go:1132 successfully dialed "wss://localhost:41591/api"
16:32:50 INFO juju.api apiclient.go:1034 cannot resolve "localhost": operation was canceled
16:32:50 INFO juju.api apiclient.go:664 connection established to "wss://localhost:41591/api"
16:32:50 INFO juju.juju api.go:328 API endpoints changed from [localhost:40511 10.152.183.101:17070] to [localhost:41591 10.152.183.101:17070]
16:32:50 INFO juju.juju api.go:78 connecting to API addresses: [localhost:41591 10.152.183.101:17070]
16:32:50 DEBUG juju.api apiclient.go:1132 successfully dialed "wss://localhost:43827/model/15eaab85-1324-484c-88b9-60c705fd7119/api"
16:32:50 INFO juju.api apiclient.go:1034 cannot resolve "localhost": operation was canceled
16:32:50 INFO juju.api apiclient.go:664 connection established to "wss://localhost:43827/model/15eaab85-1324-484c-88b9-60c705fd7119/api"
16:32:50 INFO juju.juju api.go:328 API endpoints changed from [localhost:41591 10.152.183.101:17070] to [localhost:43827 10.152.183.101:17070]
16:32:50 INFO juju.juju api.go:78 connecting to API addresses: [localhost:43827 10.152.183.101:17070]
16:32:50 DEBUG juju.api apiclient.go:1132 successfully dialed "wss://localhost:40869/api"
16:32:50 INFO juju.api apiclient.go:1034 cannot resolve "localhost": operation was canceled
16:32:50 INFO juju.api apiclient.go:664 connection established to "wss://localhost:40869/api"
16:32:50 INFO juju.juju api.go:328 API endpoints changed from [localhost:43827 10.152.183.101:17070] to [localhost:40869 10.152.183.101:17070]
16:32:50 DEBUG juju.cmd.juju.application.deployer deployer.go:372 cannot interpret as local charm: file does not exist
16:32:50 DEBUG juju.cmd.juju.application.deployer deployer.go:197 cannot interpret as a redeployment of a local charm from the controller
16:32:51 INFO juju.juju api.go:78 connecting to API addresses: [localhost:40869 10.152.183.101:17070]
16:32:51 DEBUG juju.api apiclient.go:1132 successfully dialed "wss://localhost:42843/model/15eaab85-1324-484c-88b9-60c705fd7119/api"
16:32:51 INFO juju.api apiclient.go:1034 cannot resolve "localhost": operation was canceled
16:32:51 INFO juju.api apiclient.go:664 connection established to "wss://localhost:42843/model/15eaab85-1324-484c-88b9-60c705fd7119/api"
16:32:51 INFO juju.juju api.go:328 API endpoints changed from [localhost:40869 10.152.183.101:17070] to [localhost:42843 10.152.183.101:17070]
16:32:51 DEBUG juju.api monitor.go:35 RPC connection died
16:32:52 DEBUG juju.api monitor.go:35 RPC connection died
ERROR archive file "README.md" not found
16:32:52 DEBUG cmd supercommand.go:537 error stack:
archive file "README.md" not found
github.com/juju/juju/cmd/juju/application/deployer/deployer.go:440:
github.com/juju/juju/cmd/juju/application/deployer/deployer.go:68:
github.com/juju/juju/cmd/juju/application/deploy.go:800:
```

I don't remember us *requiring* README.md (it also doesn't help that if I just create that and the 'charmcraft pack' with the released charmcraft, it does *not* include a README.md by default.

However, it seems very strange to fail a deployment because there isn't a README.md. If we do want to mandate it, then we need to make sure charmcraft pack requires it as well.

[John A Meinel (jameinel)]

https://github.com/canonical/charmcraft/issues/275

It seems we have long validated store bundles have a README.md (even though we don't validate that for local bundles). So this is more that chamcraft should be treating them as mandatory as well.