add warning that "make test" can take a long time

diff --git a/README b/README
index 31d3e9f554e868d80ac4d9a57907f8ca917df444..e619b4f2eaf68abcaf1491de0ad9dde7b408d7ec 100644 (file)
--- a/README
+++ b/README
@@ -124,7 +124,9 @@ BUILDING:
  If the desired version of 'python' is not already on your PATH, then type
  'make PYTHON=/path/to/your/preferred/python'.
 
- 'make test-all' runs the unit test suites.
+ 'make test-all' runs the unit test suites.  (This can take a long time on
+ slow computers.  There are a lot of tests and some of them do a lot of
+ public-key cryptography.)
 
 
 INSTALLING: