Update README.md for Fedora 28, fixing missing build-dep

Change-Id: Iaa29eb3e523548dd746c366f318a67e14e3683f7
Signed-off-by: Stewart Smith <stewart@linux.ibm.com>
diff --git a/README.md b/README.md
index 84eabfa..e17b8b7 100644
--- a/README.md
+++ b/README.md
@@ -21,10 +21,10 @@
 sudo apt-get install -y git build-essential libsdl1.2-dev texinfo gawk chrpath diffstat
 ```
 
-- Fedora 23
+- Fedora 28
 
 ```
-sudo dnf install -y git patch diffstat texinfo chrpath SDL-devel bitbake
+sudo dnf install -y git patch diffstat texinfo chrpath SDL-devel bitbake rpcgen
 sudo dnf groupinstall "C Development Tools and Libraries"
 ```
 ### 2) Download the source