DOC: Refer to ITK's discussion space in a consistent manner

Refer to ITK's discussion space in a consistent manner, in line with the
`CONTRIBUTING` document.

Define the link to it at a single location in the document.

Link to the discussion space in all place where it is mentioned.

CODE_OF_CONDUCT.md

@@ -60,8 +60,8 @@ unless discussing something sensitive (e.g. potential conflicts of interest).
 This applies to messages for help or project-related support, too; not only is
 a public support request much more likely to result in an answer to a question,
 it also ensures that any inadvertent mistakes in answering are more easily
-detected and corrected. Please avoid seeking for help privately; asking in the
-official ITK discussion forums will increase your chances of getting an answer.
+detected and corrected. Please avoid seeking for help privately; asking on
+[ITK's Discourse] will increase your chances of getting an answer.
 
 ### Be welcoming
 
@@ -369,8 +369,7 @@ documentation (namely, the
 [DICOM Supplement 55](ftp://medical.nema.org/medical/dicom/final/sup55_ft.pdf)
 and
 [DICOM Supplement 142](ftp://medical.nema.org/medical/dicom/final/sup142_ft.pdf)).
-If you still need help for de-identifying your images, please ask on the
-[ITK discussion](https://discourse.itk.org/).
+If you still need help for de-identifying your images, please ask on [ITK's Discourse].
 
 Please, simply avoid using images that, despite having been used in image
 analysis and related areas historically (e.g. "Lena"), may be interpreted as
@@ -430,3 +429,5 @@ licensing terms for us to easily reuse.
 
 All content on this page is licensed under a Creative Commons Attribution
 license.
+
+[ITK's Discourse]: https://discourse.itk.org/