"Getting started from the command line" examples don't all work on Windows

Some of the examples use single quotes which aren't interpreted as meaning a string arguments for Window's Command Prompts:

```
> keybase encrypt mnem -m 'a secret for myself'
usage: keybase encrypt [-h] [-r] [-l] [-a ASSERT] [--batch] [--prompt-remote]
[-s] [-m MESSAGE] [-b] [-o OUTPUT]
them [file]
keybase encrypt: error: Unrecognized arguments: secret for myself'.
```

So here it's passing the string as three arguments: `'secret`, `for` and `myself'`. A solution would be to show the examples using double quotes and then it'll work as expected (although then sane shell users might get some unexpected expansions).

Note that this only affects Command Prompt. PowerShell correctly interprets single quotes for string arguments.

Review the "Getting started from the command line" examples mentioned in the issue, starting with the `keybase encrypt mnem -m` example. Check the examples in Windows Command Prompt and PowerShell, then update the affected Command Prompt examples so their quoted string arguments work there without breaking the documented PowerShell behavior.

Written by the indexing model from the issue text.