Add skiboot-5.1.18 release notes

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

doc/release-notes/skiboot-5.1.18.txt

@@ -0,0 +1,31 @@
+skiboot-5.1.18
+--------------
+
+skiboot-5.1.18 was released on Friday 26th August 2016.
+
+skiboot-5.1.18 is the 19th stable release of 5.1, it follows skiboot-5.1.17
+(which was released July 21st, 2016).
+
+This release contains a few minor bug fixes.
+
+Changes are:
+
+All platforms:
+- opal/hmi: Fix a TOD HMI failure during a race condition.
+  Rare race condition which meant we wouldn't recover from TOD error
+
+- hw/phb3: Update capi initialization sequence
+  The capi initialization sequence was revised in a circumvention
+  document when a 'link down' error was converted from fatal to Endpoint
+  Recoverable. Other, non-capi, register setup was corrected even before
+  the initial open-source release of skiboot, but a few capi-related
+  registers were not updated then, so this patch fixes it.
+  The point is that a link-down error detected by the UTL logic will
+  lead to an AIB fence, so that the CAPP unit can detect the error.
+
+FSP platforms:
+- FSP/ELOG: Fix OPAL generated elog resend logic
+- FSP/ELOG: Fix possible event notifier hangs
+- FSP/ELOG: Disable event notification if list is not consistent
+- FSP/ELOG: Fix OPAL generated elog event notification
+- FSP/ELOG: Disable event notification during kexec