=begin text does not work as documented

**perldoc Pod::Readme** says

```
You can also specify a block in another format:
=begin readme text
...
=end readme text

This will be translated into
=begin text
...
=end text
and will only be included in README files of that format.
```

I can't get any variation on that theme to produce output for text format.

I would like to select based on any output format - not just text. E.g. **=begin markdown** should output only if run with **_-f markdown_**.

Also, should there be an **=for readme text** variant? Like =for start/stop, this would allow other translators to include text common to doc and readme.

Here is a simple text case:

```
=pod

=begin text

This is text.

=end text

everywhere text.

=begin :readme

in readme

=begin text

nested text only readme

=end text

more readme

=end :readme

final

=cut

```

The results don't include any text in the **=begin text** blocks:

```
pod2readme -c -t readme -f text test.pod
everywhere text.

in readme

more readme

final

```