Updated README

Author: mumez

README.md

@@ -1,5 +1,6 @@
 msgpack-smalltalk
 =================
+[![CI](https://github.com/msgpack/msgpack-smalltalk/actions/workflows/main.yml/badge.svg)](https://github.com/msgpack/msgpack-smalltalk/actions/workflows/main.yml)
 
 MessagePack serialization library for various Smalltalk dialects.
 
@@ -8,7 +9,7 @@ MessagePack serialization library for various Smalltalk dialects.
 - VisualWorks
 - VA Smalltalk
 - Dolphin Smalltalk
-- GNU Smalltalk (Beta)
+- GNU Smalltalk (Beta)
 - [Cuis](https://github.com/mumez/Cuis-Smalltalk-MessagePack)
 
 Sources are put as [Cypress](https://github.com/CampSmalltalk/Cypress/blob/master/README.md) for the neutral accesses from various Smalltalk dialects.
@@ -63,15 +64,15 @@ Please read [HowToInstall.md](<https://github.com/msgpack/msgpack-smalltalk/blob
 
 ### Loading the latest development version
 
-#### Squeak
+#### Squeak 4
 ```Smalltalk
 Installer squeaksource
     project: 'MessagePack';
     install: 'ConfigurationOfMessagePack'. 
 (Smalltalk at: #ConfigurationOfMessagePack) project development load
 ```
 
-#### Pharo
+#### Pharo & Squeak 5+
 ```Smalltalk
 Metacello new
   repository: 'github://msgpack/msgpack-smalltalk/repository';
@@ -81,4 +82,7 @@ Metacello new
 
 You might need ```MpTypeMapper initializeAll ``` on new encoder/decoder-related updates.
 
+#### Limitation on Squeak 5+
 
+Starting with Squeak 5 and 6, DateAndTime only supports microsecond precision. Because of this, nanosecond values are not properly decoded as DateAndTime.
+Two unit tests (testPackUnpackTimestamp64, 96) fail on Squeak 5 and 6.