PEL: Add sysinfo UserData section to README

Mention the UserData section that is added to every BMC PEL that
contains system information in the README where it lists the sections
created.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: If36396817f438bc97785a0a60c18e11c7c276ac1
diff --git a/extensions/openpower-pels/README.md b/extensions/openpower-pels/README.md
index bf3e260..e5fd2b6 100644
--- a/extensions/openpower-pels/README.md
+++ b/extensions/openpower-pels/README.md
@@ -65,6 +65,10 @@
   - If the AdditionalData property in the OpenBMC event log has anything in it,
     it will be saved in a UserData section as a JSON string.
 
+- System information
+  - This section contains various pieces of system information, such as the
+    full code level and the BMC, chassis, and host state properties.
+
 ## The PEL Message Registry
 
 The PEL message registry is used to create PELs from OpenBMC event logs.