CONTRIBUTING.rst

@@ -27,7 +27,7 @@ You can also submit patches via *merge request* to Salsa, Debian's Gitlab. Start
 by forking the `diffoscope Git
 repository <https://salsa.debian.org/reproducible-builds/diffoscope>`__
 (see
-`documentation <https://salsa.debian.org/help/gitlab-basics/fork-project.md>__`),
+`documentation <https://salsa.debian.org/help/gitlab-basics/fork-project.md>`__),
 make your changes and commit them as you normally would. You can then push your
 changes and submit a *merge request* via Salsa.  See `Gitlab documentation
 <https://salsa.debian.org/help/gitlab-basics/add-merge-request.md>`__ about
@@ -52,6 +52,23 @@ The ``format-patch`` command will create a series of ``.patch`` files in your
 checkout. Attach these files to your submission in your e-mail client or
 reportbug.
 
+Add a comparator
+================
+
+Diffoscope doesn't support a specific file type? Please contribute to the
+project! Each file type is handled by a comparator, and writing a new one is
+usually very easy.
+Here are the steps to add a new comparator:
+
+- Add the new comparator in ``diffoscope/comparators/`` (have a look at the
+  other comparators in the same directory to have an idea of what to do)
+- Declare the comparator File class in ``ComparatorManager`` in
+  ``diffoscope/comparators/__init__.py``
+- Add a test in ``tests/comparators/``
+- If required, update the ``Build-Depends`` list in ``debian/control``
+- If required, update the ``EXTERNAL_TOOLS`` list in
+  ``diffoscope/external_tools.py``
+
 Uploading the package
 =====================