Fix the `WriteANewExample` documentation section references

The section references in the [WriteANewExample.rst](https://github.com/InsightSoftwareConsortium/ITKExamples/blob/master/Documentation/Contribute/WriteANewExample.rst) contributing documentation file seem not to be correctly built/do not point to the desired anchor and are not correctly rendered. e.g.
```
In this section we describe how to write an example by walking through the sections of an
example's reStructuredText file. The mechanics of submitting an example via
:ref:`Git/Gerrit directly ` are covered in other sections.
```
points to `https://github.com/InsightSoftwareConsortium/ITKExamples/blob/master/Documentation/Contribute/WriteANewExample.rst#id1`
or
```
For this reason, we recommend to use the provided python script CreateNewExample.py see
:ref:`CreateNewExample`
```
points to `https://github.com/InsightSoftwareConsortium/ITKExamples/blob/master/Documentation/Contribute/WriteANewExample.rst#id3`

Start with Documentation/Contribute/WriteANewExample.rst and inspect the :ref: references shown in the issue, including text-editor-submission and CreateNewExample. Check how the Sphinx documentation renders these references and verify that the generated links point to the intended section anchors rather than generic ids.

Written by the indexing model from the issue text.