update build guides

readme.md

@@ -27,24 +27,29 @@ Realm can be run in a container with OCI (like Docker, Podman, Kubernetes, etc),
 
 ## Build Guides
 
-Install rust toolchains with [rustup](https://rustup.rs/).
+Install rust **nightly** toolchains with [rustup](https://rustup.rs/):
 
 ```shell
 curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
 ```
 
-Clone this repository
+Clone this repository:
 
 ```shell
 git clone https://github.com/zhboner/realm
 ```
 
-Enter the directory and build
+Enter the directory and build:
 
 ```shell
 cd realm
 git submodule sync && git submodule update --init --recursive
+
+# build release
 cargo build --release
+
+# allow more possible optimizations, make it even faster
+RUSTFLAGS='-C target_cpu=native' cargo build --release
 ```
 
 ### Build Options