Document how to handle multiple mainline versions of a version

source/contributor/guidelines.rst

@@ -783,3 +783,29 @@ a distribution mechanism for packages, so it is not appropriate for software
 development work on a package (like supporting an additional platform) to be
 exclusivly performed in the Bioconda repo. It's important to engage the
 upstream authors on such efforts if at all possible.
+
+Updating multiple software major versions simultaneously
+----------------------------------------------------------
+
+In some cases, a particular software package may support updates and patches for
+two major versions of a tool at the same time.
+For example, a developer continues relasing fixes to v2.x series, even if most 
+development continues on a v3.x series.
+
+To continue to support releases of both versions of a tool within a Bioconda
+recipe, use the main recipe `meta.yaml` for the more recent major version,
+and place the older version in a subdirectory with it's own `meta.yaml`.
+
+An example of this is the `mitos
+<https://github.com/bioconda/bioconda-recipes/tree/c2b7cbc80054a309e8fc3c91f9efed4e642e447d/recipes/mitos>`_ package.
+
+.. code-block:: yaml
+
+    recipes/mitos
+    ├── meta.yaml
+    └── mitos1
+        └── meta.yaml
+
+The original `mitos` v1 recipe is under the `mitos1/` directory, but the
+`meta.yaml` for the more recent v2 file is in a dedicated sub directory.
+