Update copilot-instructions.md

Author: JonnyBurger

.github/copilot-instructions.md

@@ -6,6 +6,7 @@ The **package name** for each folder is `@remotion/[folder-name]`, except for th
 
 ## Build instructions
 
+- `pnpm` is the package manager for the project.
 - To build the project after you made changes, run `bunx turbo make --filter="[package-name]"` and only include the package you are working on. Refer to package naming convention above. For example, the command to build the package in `packages/shapes` is `bunx turbo make --filter="@remotion/shapes"`.
 
 ## Documentation