[xs] Helpful SOLR hint.

doc/solr-setup.rst

@@ -192,6 +192,18 @@ Some problems that can be found during the install:
 
     <dataDir>${dataDir}</dataDir>
 
+* When running Solr it says `Unable to find a javac compiler; com.sun.tools.javac.Main is not on the classpath. Perhaps JAVA_HOME does not point to the JDK.`
+
+ See the note above about JAVA_HOME. Alternatively you may not have installed the JDK. Check by seeing if javac is installed::
+   
+     which javac
+
+ If it isn't do::
+
+     sudo apt-get install openjdk-6-jdk
+
+ and restart SOLR.
+
 Handling changes in the CKAN schema
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