update installation scripts and docs

doc/_readme/scripts/install_macos.sh

@@ -1,8 +1,7 @@
 # shellcheck disable=all
-DIR=$(cd "$(dirname "$0")" && pwd)
 brew update
 brew install llvm@19 lld@19 bdw-gc openssl cjson libffi libuv pkg-config
 brew install python@3.12 # optional
 brew link --overwrite lld@19 libffi
 # curl https://raw.githubusercontent.com/goplus/llgo/refs/heads/main/install.sh | bash
-cat ${DIR}/../../../install.sh | bash
+./install.sh