[CLI] - Provide CLI command examples with options

This page could be more helpful with working examples for the various commands.

As a reference, it omits necessary information such as the requirement to supply a cluster with '-c' so that the commands will actually work as expected.

Consider using the examples from the output of `couchbase-cli -h` in this documentation to make it more useful.

Note also that the authentication options -u and -p are needed for most commands and the syntax of the options should be demonstrated as the command option handling is finicky about ordering.

It would also be helpful to note in the subcommand tables, which subcommands can be performed as the read-only user and which require the administrator user.

Some command line examples:

server-list (can be performed as read-only user or Administrator user):

```
couchbase-cli server-list -u readonly -p 654321 -c brian.local:8091
```

server-info (can be performed as read-only user or Administrator user):

```
couchbase-cli server-info -u Administrator -p 123456 -c brian.local:8091
```

rebalance (requires Administrator user):

```
couchbase-cli rebalance -u Administrator -p couchbase -c centos-0663-brian.local:8091
```