[meta-xilinx] [PATCH 2/2] README: improve layer requirements info

[Jean-Francois Dagenais]

The previous wording implies that the working shell's PATH must contain
the SDK's path, which is not the case. The layer's classes add the
proper SDK bin dir to the PATH at tool invokation.

Also clarify things about the XILINX_VER_MAIN and XILINX_SDK_TOOLCHAIN
variables.

Signed-off-by: Jean-Francois Dagenais <jeff.dagenais at gmail.com>
---
 README.md | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 30616ed..2acd4aa 100644
--- a/README.md
+++ b/README.md
@@ -22,10 +22,15 @@ Dependencies
 
 This layer depends on:
 
-XSCT being installed in your path
+XSCT being installed somewhere the yocto build can access. You must define
+this path by specifying the XILINX_SDK_TOOLCHAIN variable globally, typically
+in your local.conf (or site.conf).
 
-Define the PATH using the variable XILINX_SDK_TOOLCHAIN
-The supported tool version is indicated in XILINX_VER_MAIN
+The supported tool version is indicated in XILINX_VER_MAIN which defaults to
+the current release that is checked out.
+
+It would be wise then to define XILINX_SDK_TOOLCHAIN like so:
+XILINX_SDK_TOOLCHAIN = "/full/path/to/xilinx/SDK/${XILINX_VER_MAIN}"
 
 Each release is dependent on the Xilinx XSCT release version. Please note that
 xsct tools may not be backward compatible with embeddedsw repo. Meaning
-- 
2.1.4