README: note the vivado version requirements

diff --git a/README.md b/README.md
index 940b3d0b02907e3a3db6d6889e7b9f889501cd0f..3ba50116d80d40c21b9d808a67043492c2a8779f 100644 (file)
--- a/README.md
+++ b/README.md
@@ -44,6 +44,8 @@ $ make -f Makefile.e300artydevkit verilog
 $ make -f Makefile.e300artydevkit mcs
 ```
 
+Note: This flow requires vivado 2017.1. Old versions are known to fail.
+
 These will place the files under `builds/e300artydevkit/obj`.
 
 Note that in order to run the `mcs` target, you need to have the `vivado`
@@ -77,6 +79,8 @@ $ make -f Makefile.u500vc707devkit verilog
 $ make -f Makefile.u500vc707devkit mcs
 ```
 
+Note: This flow requires vivado 2016.1. Newer versions are known to fail.
+
 These will place the files under `builds/u500vc707devkit/obj`.
 
 Note that in order to run the `mcs` target, you need to have the `vivado`