Re-phrase note about jattool-minimal

The assumption that RHEL-6 and older don't have Jinja2 was incorrect;
just the package is named differently.  However, in many cases people
will still want small installs, so we're keeping the split, just the
note is rephrased to be more accurate.

README.md

@@ -69,12 +69,14 @@ Older distros like CentOS 6 and 7, don't have `dnf copr` or `yum copr` plugin,
 so you'll have to pick correct *.repo* file from COPR site and download it
 under */etc/yum.repos.d*.
 
-Also, older distros also necessarily have all dependencies available, so if you
-only want to *run* test (but not eg. export to HTML), you only need to install
-*jattool-minimal*:
+Note that on testing machines, where you only want to *run* test (but not eg.
+export to HTML), you only need to install *jattool-minimal*:
 
     # yum install jattool-minimal
 
+This will help you avoid excess dependencies.  Test suites should also normally
+depend only on *jattool-minimal*.
+
 
 ### Installation -- Debian and similar ###