README.md in oxidized-0.26.1 vs README.md in oxidized-0.26.2

- old
+ new

@@ -102,10 +102,10 @@
 
 Install Ruby 2.3 from [SCL](https://www.softwarecollections.org/en/scls/rhscl/rh-ruby23/):
 
 ```shell
 yum install centos-release-scl
-yum install rh-ruby23
+yum install rh-ruby23 rh-ruby23-devel
 scl enable rh-ruby23 bash
 ```
 
 The following additional packages will be required to build the dependencies:
 