workspace: add .vscode settings

This configures the VSCode rust-analyzer plugin to provide hints under
'sources/'. Without this configuration, rust-analyzer is tripped up by
`buildsys` build scripts under 'packages/'.

We also insert a final newline in text files to ensure POSIX compliance.

Author: cbgbt

.vscode/settings.json

@@ -0,0 +1,6 @@
+{
+    "rust-analyzer.linkedProjects": [
+        "sources/Cargo.toml"
+    ],
+    "files.insertFinalNewline": true
+}