docs: clarify that setup commands run as root and repo location

- Add information about setup commands running as root user
- Specify that repositories are cloned to /workspace directory
- Add example for running commands as non-root user (e.g., for Homebrew)

Co-authored-by: Jay Hack <jay@codegen.com>

Author: codegen-sh[bot]

docs/sandboxes/setup-commands.mdx

@@ -31,6 +31,13 @@ To configure setup commands for a repository:
 
 Enter your desired setup commands in the provided text area, with one command per line. These commands will be executed in sequence within the sandbox environment.
 
+<Info>
+  **Important Environment Details:**
+  - All setup commands run as the **root** user
+  - Your repository is cloned to the **/workspace** directory
+  - If you need to run commands as a non-root user, use `su <username> -c "command"` (e.g., `su linuxbrew -c "brew install <package>"`)
+</Info>
+
 For example, you might want to:
 
 - Switch to a specific Node.js version.
@@ -67,6 +74,12 @@ npm ci
 npm run build
 ```
 
+```bash
+# Running commands as a non-root user (e.g., for Homebrew)
+su linuxbrew -c "brew install postgresql"
+su linuxbrew -c "brew services start postgresql"
+```
+
 ### Working with Different Python Versions
 
 The sandbox comes with Python 3.13 by default, but some packages may not yet be compatible with this version. Here are strategies for handling different Python versions:
@@ -144,4 +157,3 @@ deactivate
   The environment variables listed in the "Env Variables" section are available
   during the execution of these setup commands.
 </Tip>
-