download: fix nvm instructions

Fixes #7433

Author: ljharb

apps/site/snippets/en/download/nvm.bash

@@ -4,6 +4,9 @@ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.1/install.sh | bash
 # Download and install Node.js:
 nvm install ${props.release.major}
 
+# activate nvm (in lieu of restarting the shell)
+\. "${HOME}/.nvm/nvm.sh"
+
 # Verify the Node.js version:
 node -v # Should print "${props.release.versionWithPrefix}".
 nvm current # Should print "${props.release.versionWithPrefix}".