add minimal working example

cypress/e2e/hedgedoc-migrator.cy.js

@@ -0,0 +1,31 @@
+async function getContent(url) {
+  const res = await fetch(url.concat('/download'));
+  return res.text();
+}
+
+async function migrateDocument(url, baseUrl) {
+  const content = await getContent(url);
+  cy.request({
+    url: baseUrl.concat('/new'),
+    method: 'POST',
+    headers: {
+      'Content-Type': 'text/markdown',
+      'Access-Control-Allow-Origin': new URL(baseUrl).hostname,
+    },
+    body: content,
+  }).then((res) => {
+    const redirect = res.redirects[0].split(' ')[1];
+    cy.visit(url);
+    cy.get('#view-mode-toggle-edit').click({force: true});
+    cy.get('.CodeMirror-scroll').type('{ctrl}a{backspace}');
+    cy.get('.CodeMirror-scroll').type(`Moved to [${redirect}](${redirect})`);
+  });
+}
+
+describe('Migrate document', () => {
+  it('passes', async () => {
+    const baseUrl = 'https://md.margau.net';
+    const url = 'https://md.margau.net/H0JO3L5DS-6Yhv4RrdS-tw';
+    migrateDocument(url, baseUrl);
+  });
+});