Clear up confusions around installing LLVM/clang in doc

guide/src/overview.md

@@ -3,35 +3,31 @@
 `emacs-module-rs` provides high-level Rust binding and tools to write Emacs's dynamic modules. It is easy to use if you know either Rust or Emacs.
 
 It currently supports:
-- Stable Rust 1.38+.
+- Stable Rust 1.45+.
 - Emacs 25 or above, built with module support.
 - macOS, Linux, Windows.
 
-## Known Issues
-
-There is a bug (see [issue #1](https://github.com/ubolonton/emacs-module-rs/issues/1)) with Emacs 26 on Linux that prevents it from loading any dynamic modules (even those written in C), if:
-- Emacs is built without thread support.
-- The OS is Ubuntu 16.04 (Xenial).
-
 ## Setting up
 
 - Install the Rust toolchain with [rustup](https://www.rustup.rs/).
-- Install `clang`. This is needed to generate the raw binding from `emacs-module.h`.
 - Make sure that your Emacs was compiled with module support. Check that `module-file-suffix` is not `nil`, and the function `module-load` is defined.
   + On macOS, the recommended installation method is MacPorts (`emacs-app` and `emacs-mac-app`).
   + On Windows, the recommended installation method for older Emacs versions (before 27.2) is `pacman -S mingw-w64-x86_64-emacs` (msys2), as the archives on GNU FTP's server were built without module support.
 
-### Windows
-This was only tested with Rust's `msvc` toolchain, not the `gnu` toolchain.
+### Notes
 
-For older versions of the crate (before 0.18.0), or when the optional feature `bindgen` is enabled, you will also need to install LLVM and set `LIBCLANG_PATH` accordingly.
+- On Windows, only Rust's `msvc` toolchain was confirmed to work, not the `gnu` toolchain.
+- When the optional feature `bindgen` is enabled, the raw binding will be generated from `emacs-module.h` at build time. Therefore you will also need to install `clang`. (This is recommended only for troubleshooting, though.) For example, on Windows:
+    ```powershell
+    # In Powershell
+    scoop install llvm
 
-```powershell
-# In Powershell
-scoop install llvm
+    $env:LIBCLANG_PATH = "$(scoop prefix llvm)\bin"
+    cargo build --all
+    ```
 
-$env:LIBCLANG_PATH = "$(scoop prefix llvm)\bin"
-cargo build --all
+## Known Issues
 
-.\bin\test.ps1
-```
+There is a bug (see [issue #1](https://github.com/ubolonton/emacs-module-rs/issues/1)) with Emacs 26 on Linux that prevents it from loading *any dynamic modules* (even those written in C), if:
+- Emacs is built without thread support.
+- The OS is Ubuntu 16.04 (Xenial).