Issue 6695 - Allow automatically downloading V8

README.md

Index: README.md
===================================================================
--- a/README.md
+++ b/README.md
@@ -43,31 +43,46 @@
 * g++ multilib
 
 If you have a compilation issue with another compiler please [create an issue](https://issues.adblockplus.org/).
 
 You also need Python 2.7 and ensure that `python.exe` is in your `PATH`.
 
 ### Unix
 
+You need V8 prior to building. Two options:
+
+* Use the default prebuild V8 by invoking the make target
+`get-prebuild-v8`. This will download and extract the prebuild V8 for
+your setup. The default environment will be set by the Makefile at
+build time. If you are cross compiling use the same options as below
+to invoke make.
+
+If you switch target platform using the same source tree, you should
+manually remove the `third_party/prebuilt-v8` directory and redownload
+again with the right options.
+
+Or
+
 * Prepare V8 and set environment variables LIBV8_LIB_DIR and LIBV8_INCLUDE_DIR.
 LIBV8_INCLUDE_DIR should point to the include directory of V8, e.g.
 `.../v8/include` and there should be `libv8_monolith.a` in the directory
 LIBV8_LIB_DIR.
 
+To build:
+
 Using Make:
 
     make
 
 The default target architecture is the architecture of a host. In order to build for a different architecture pass `TARGET_ARCH` to `make`, e.g. run:
 
     make TARGET_ARCH=ia32
 
 supported values are `ia32` and `x64`.
-    
 
 To build and run the tests:
 
     make test
 
 Likewise, use the following with `TARGET_ARCH`:
 
     make test TARGET_ARCH=ia32