docs: add troubleshooting permission denied (janhq#1631)

docs: add troubleshooting permission denied

docs/docs/guides/08-troubleshooting/05-permission-denied.mdx

@@ -0,0 +1,32 @@
+---
+title: Permission Denied
+slug: /troubleshooting/permission-denied
+description: Permission denied.
+keywords:
+  [
+    Jan AI,
+    Jan,
+    ChatGPT alternative,
+    local AI,
+    private AI,
+    conversational AI,
+    no-subscription fee,
+    large language model,
+    troubleshooting,
+    permission denied,
+  ]
+---
+
+When you run Jan, you may encounter the following error:
+
+```bash
+Uncaught (in promise) Error: Error invoking layout-480796bff433a3a3.js:538 remote method 'installExtension':
+Error Package /Applications/Jan.app/Contents/Resources/app.asar.unpacked/pre-install/janhq-assistant-extension-1.0.0.tgz does not contain a valid manifest:
+Error EACCES: permission denied, mkdtemp '/Users/username/.npm/_cacache/tmp/ueCMn4'
+```
+
+This error indicates a permission issue during the installation process. To fix this issue, you can run the following command to change ownership of the `~/.npm` directory to the current user:
+
+```bash
+sudo chown -R $(whoami) ~/.npm
+```