docs: create setup documentation

Author: davidkurilla

src/tools/rust-analyzer/docs/dev/setup.md

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+# Setup Guide
+
+This guide gives a simplified opinionated setup for developers contributing to rust-analyzer.
+
+## Prerequisites
+
+Since rust-analyzer is a Rust project, you will need to install Rust. You can download and install the latest stable version of Rust [here](https://www.rust-lang.org/tools/install).
+
+You will also need Visual Studio Code and Visual Studio Code Insiders for this workflow. You can download and install Visual Studio Code [here](https://code.visualstudio.com/Download) and you can download and install Visual Studio Code Insiders [here](https://code.visualstudio.com/insiders/).
+
+You will also need to install the rust-analyzer extension for Visual Studio Code and Visual Studio Code Insiders.
+
+More information about Rust on Visual Studio Code can be found [here](https://code.visualstudio.com/docs/languages/rust)
+
+## Step-by-Step Setup
+
+**Step 01**: Fork the rust-analyzer repository and clone the fork to your local machine.
+
+**Step 02**: Open the project in Visual Studio Code.
+
+**Step 03**: Open a terminal and run `cargo build` to build the project.
+
+**Step 04**: Install the language server locally by running the following command:
+
+```sh
+cargo xtask install --server --code-bin code-insiders --dev-rel
+```
+
+In the output of this command, there should be a file path provided to the installed binary on  your local machine.
+It should look something like the following output below
+
+```
+Installing <path-to-rust-analyzer-binary>
+Installed package `rust-analyzer v0.0.0 (<path-to-rust-analyzer-binary>)` (executable `rust-analyzer.exe`)
+```
+
+In Visual Studio Code Insiders, you will want to open your User Settings (JSON) from the Command Palette. From there you should ensure that the `rust-anaylzer.server.path` key is set to the `<path-to-rust-analyzer-binary>`. This will tell Visual Studio Code Insiders to use the locally installed version that you can debug.
+
+The User Settings (JSON) file should contain the following:
+
+```json
+{
+    "rust-analyzer.server.path": "<path-to-rust-anaylzer-binary>"
+}
+```
+
+Now you should be able to make changes to rust-analyzer in Visual Studio Code and then view the changes in Visual Studio Code Insiders.
+
+## Debugging rust-analyzer
+The simplist way to debug rust-analyzer is to use the `eprintln!` macro. The reason why we use `eprintln!` instead of `println!` is because the language server uses `stdout` to send messages. So instead we will debug using `stderr`.
+
+An example debugging statement could go into the `main_loop.rs` file which can be found at `crates/rust-analyzer/src/main_loop.rs`. Inside the `main_loop` we will add the following `eprintln!` to test debugging rust-analyzer:
+
+```rs
+eprintln!("Hello, world!");
+```
+
+Now we run `cargo build` and `sh
+cargo xtask install --server --code-bin code-insiders --dev-rel` to reinstall the server.
+
+Now on Visual Studio Code Insiders, we should be able to open the Output tab on our terminal and switch to Rust Analyzer Language Server to see the `eprintln!` statement we just wrote.
+
+If you are able to see your output, you now have a complete workflow for debugging rust-analyzer.