Update README

Add rustup instructions to install rustc and cargo

README.md

@@ -2,14 +2,29 @@
 
 ## Build instructions
 
-You need rust installed, with rustup as its the simple thing to do.
+You need rust installed, with rustup as its the simple thing to do. To install
+rust, use the following command then add the `$HOME/.cargo/bin` folder to your
+path:
 
-Just use the `cargo build` command. You will need the nighly version of the rust
-toolchain, so a `rustup default nightly` might be needed.
+```bash
+# Install rustup
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
+# Or, if rustup is already installed :
+rustup update
+```
+
+To build, just use the `cargo build` command. You will need the nighly version
+of the rust toolchain, so a `rustup default nightly` might be needed.
+
+If you need `rls` (Rust Language Server) and it's missing from the nightly
+builds, you can find the latest nightly build that has that compoment at:
+https://rust-lang.github.io/rustup-components-history/ and install that specific
+version with `rustup install nightly-2021-12-05`.
 
 ## Help
 
-Here are the matrix sdk samples: https://github.com/matrix-org/matrix-rust-sdk/tree/main/crates/matrix-sdk/examples
+Here are the matrix sdk samples:
+https://github.com/matrix-org/matrix-rust-sdk/tree/main/crates/matrix-sdk/examples
 
 ## TODO