add don't delete your sheet warning

Author: JoeGermuska

website/_make.njk

@@ -274,6 +274,7 @@ https://cdn.knightlab.com/libs/timeline3/latest/embed/index.html?source=1xuY4upI
                     </form>
                     <a class="button button-complement" href="#preview-embed" id="iframe-preview-button">Preview</a>&nbsp;
                     <a class="button button-light" href="#" id="preview-embed-link" target="_blank">Open Preview in a new window  &nbsp;<span class="icon-new-tab"></span></a>
+                    <p class="note">Every time a timeline is viewed, the data is loaded from Google Sheets. This means that if you need to change your timeline, you don't need to come back and do anything here, or even republish it. Just edit Google Sheets. <br><br>This also means that <strong style="color: #444">you should never delete the Google Sheets document that configures a published timeline!</strong> Knight Lab cannot help you recover a deleted configuration spreadsheet.</p>
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