Update README.md (paritytech#28)

Fixes paritytech#26
Fixes paritytech#27

Author: athei

.github/workflows/build_and_release.yml

@@ -4,6 +4,8 @@ on:
   push:
     branches:
       - main
+    paths-ignore:
+      - README.md
 
 permissions:
   contents: write

README.md

@@ -2,19 +2,41 @@
 
 This repository compile and publish as release final binaries of the Rust toolchain targetting RISC-V RV32E.
 
-## Download 
+## Building
+
+```sh
+./clone.sh
+./patch.sh
+./build.sh
+./package.sh
+```
+
+Executing those steps will create a `rust-rve-nightly-$rust_commit_date-$TOOLCHAIN_HOST_TRIPLET.xz` in your working directory. See the next chapter about installation how to use this
+toolchain with rustup.
+
+## Installation
+
+You can either download a package from the release page or build it yourself with the instructions above. The following steps will make the toolchain available via rustup's
+`+rve-nightly` syntax.
 
 ``` sh
-# Download the latest release from the release page.
-tar --zstd -xf rust-rve-nightly-2023-04-05-aarch64-apple-darwin.tar.zst
+tar --zstd -xf rust-rve-nightly-$rust_commit_date-$TOOLCHAIN_HOST_TRIPLET.xz
 mv rve-nightly ~/.rustup/toolchains/
+# Clear the "downloaded" attribute recursively on macOS to satisfy GateKeeper
+xattr -rc ~/.rustup/toolchains/rve-nightly
 ```
 
+The last step is needed when downloading the binary toolchain with Safari. Otherwise GateKeeper will prevent running downloaded binaries without code signature:
+
+<img width="245" alt="326768663-26a8b06f-5074-485e-9677-12806b0454bd" src="https://github.com/paritytech/rustc-rv32e-toolchain/assets/2580396/5fd140ae-526c-435c-8e6c-ba91a3ab27d3">
+
 ## Build with `ci-unified`
 
 If there is a need to build the toolchain using [Parity default CI environment](https://github.com/paritytech/scripts/tree/master/dockerfiles/ci-unified), tweak the build step as follows:
 
 ```
 export CXX=/usr/bin/clang++-15
+...
 ./build.sh --DCMAKE_BUILD_TYPE=Release
+...
 ```