docs: add version error to common errors

www/docs/errors/version.md

@@ -0,0 +1,24 @@
+# Configuration version errors
+
+This can show as an error or as an warning:
+
+```
+only configurations files on version: 2 are supported, yours is version: 0, please update your configuration
+```
+
+It has to do with the v2 update.
+
+If you get it as a warning, your configuration file is valid in v2, but would
+benefit with the version header.
+You can remove the warning by adding this line to your configuration:
+
+```yaml
+version: 2
+```
+
+If you get it as a fatal error, it means your configuration is invalid.
+You can still add the `version` header mentioned above, and it'll tell you which
+parts of the configuration need to be fixed.
+
+You can check the [deprecations](../deprecations.md) page to see how to fix
+them.

www/mkdocs.yml

@@ -187,6 +187,7 @@ nav:
       - users.md
       - deprecations.md
       - Common errors:
+          - errors/version.md
           - errors/dirty.md
           - errors/multiple-tokens.md
           - errors/release-upload.md