Update README.md

README.md

@@ -42,6 +42,14 @@ You can add `--depth 1` to the previous commands to improve the update speed but
 1. Add author's info in `./slides/intro.html` and `./slides/outro.html`
 1. Put your content in `./slides/content.md` or add slides files in `./slides/` and link these in `./index.html`
 
+All user-supplied content MUST be placed under the `slides` directory.
+
+This allows to easily merge changes from this template without breaking the
+slides.
+
+If you're updating old slides you should resolve all the conflicts yourself and
+migrate to the new layout described here.
+
 ### How do I write my stuff?
 
 Using Vim.