doc: Add historical release notes for 0.5.1

docs/release-notes/release-notes-0.5.1.md

@@ -0,0 +1,41 @@
+Elastos.ELA version 0.5.1 is now available from:
+
+  <https://download.elastos.org/elastos-ela/elastos-ela-v0.5.1/>
+
+This is a new minor version release, check and clean transactions in transaction pool after the status has changed. 
+
+Please report bugs using the issue tracker at GitHub:
+
+  <https://github.com/elastos/Elastos.ELA/issues>
+
+How to Upgrade
+==============
+
+If you are running version release_v0.5.0 and before, you should shut it down and wait until
+ it has completely closed, then just copy over `ela` (on Linux).
+
+However, as usual, config, keystore and chaindata files are compatible.
+
+Compatibility
+==============
+
+Elastos.ELA is supported and extensively tested on operating systems
+using the Linux kernel. It is not recommended to use Elastos.ELA on
+unsupported systems.
+
+Elastos.ELA should also work on most other Unix-like systems but is not
+as frequently tested on them.
+
+As previously-supported CPU platforms, this release's pre-compiled
+distribution provides binaries for the x86_64 platform.
+
+Notable changes
+===============
+
+Check and clean transactions in transaction pool after the status has changed 
+
+0.5.1 change log
+=================
+
+- #1530 Check and clean transactions in transaction pool after the status has changed 
+