Put quotes around manifest license examples.

Manifest.md

@@ -42,11 +42,11 @@ If you publish the source code in a git repository, it is recommended to add a g
 
 The license of your plugin.
 
-For open-source plugins, use the license identifier string from the [SPDX License List](https://spdx.org/licenses/), such as `GPL-3.0-or-later`, `GPL-3.0-only`, `MIT`, `BSD-3-Clause`, `CC0-1.0`, etc.
+For open-source plugins, use the license identifier string from the [SPDX License List](https://spdx.org/licenses/), such as `"GPL-3.0-or-later"`, `"GPL-3.0-only"`, `"MIT"`, `"BSD-3-Clause"`, `"CC0-1.0"`, etc.
 
-For freeware plugins, use `proprietary` (TODO: use `https://vcvrack.com/freeware-eula` when available) or your own freeware license URL.
+For freeware plugins, use `"proprietary"` (TODO: use `https://vcvrack.com/freeware-eula` when available), or your own freeware license URL.
 
-For commercial plugins, use `https://vcvrack.com/eula` if sold on the VCV Library or your own commercial license URL.
+For commercial plugins, use `"https://vcvrack.com/eula"` if sold on the VCV Library, or your own commercial license URL.
 
 ## `.brand`
 *String. Optional.*