[Readme] Update v8 instructions for Linux

Author: tonyfreeman

README.md

@@ -63,30 +63,20 @@ swift test \
  --generate-linuxmain
 ```
 
-### Linuxbrew
-
-#### V8
-
-```bash
-brew tap tris-brew/linux
-brew install libv8
-```
-
-#### SwiftPM arguments
-
-```bash
-export LD_LIBRARY_PATH=/home/linuxbrew/.linuxbrew/lib/
-swift build -Xcc -I/home/linuxbrew/.linuxbrew/include -Xlinker -L/home/linuxbrew/.linuxbrew/lib -Xlinker -lv8_libbase -Xlinker -lv8_libplatform
-swift test -Xcc -I/home/linuxbrew/.linuxbrew/include -Xlinker -L/home/linuxbrew/.linuxbrew/lib -Xlinker -lv8_libbase -Xlinker -lv8_libplatform
-```
-
 ### Linux
 
 #### V8
 
+For full instructions follow https://v8.dev/docs/build
 ```bash
-add-apt-repository -y ppa:pinepain/libv8
-apt update && apt install -y libv8-6.6-dev
+git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
+export PATH=$PATH:$(pwd)/depot_tools
+fetch v8
+cd v8
+gclient sync -r 7.0.276.28
+./build/install-build-deps.sh #OMG
+gn gen --args="is_debug=false is_component_build=true v8_use_external_startup_data=false v8_enable_i18n_support=false" out.gn/x64.release
+ninja -j8 -C out.gn/x64.release -v d8
 ```
 
 #### JavaScriptCore