Documentation: Add instructions for configuring the Helix editor

Documentation/HelixConfiguration.md

@@ -0,0 +1,18 @@
+# Helix Configuration
+Helix comes with support for `clangd` and `clang-format` out of the box! However, a small bit of configuration is needed for it to work correctly with SerenityOS.
+
+The following `.clangd` should be placed in the project root:
+```yaml
+CompileFlags:
+  CompilationDatabase: Build/x86_64 # Or whatever architecture you're targeting, e.g. aarch64
+  Add: [-D__serenity__]
+```
+
+You also need to configure the clangd server to detect headers properly from the Serenity toolchain. To do this, create a `.helix/languages.toml` file in the project root:
+```toml
+[[language]]
+name = "cpp"
+language-server = { command = "clangd", args=["--query-driver=/path/to/serenity/Toolchain/Local/**/*", "--header-insertion=never"] }
+```
+
+> Make sure to replace `/path/to/serenity` with the actual path in the snippet above!