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

doc/_readme/scripts/install_ubuntu.sh

@@ -5,4 +5,4 @@ sudo apt-get update
 sudo apt-get install -y llvm-19-dev clang-19 libclang-19-dev lld-19 pkg-config libgc-dev libssl-dev zlib1g-dev libcjson-dev libsqlite3-dev libunwind-dev libuv1-dev
 sudo apt-get install -y python3.12-dev # optional
 #curl https://raw.githubusercontent.com/goplus/llgo/refs/heads/main/install.sh | bash
-cat ../../../install.sh | bash
+./install.sh