Update README.md

* Description for RC5
* Hint for deprecated Arduino versions

README.md

 Future development (Marlin 1.2 and beyond) takes place in the [MarlinDev repository](https://github.com/MarlinFirmware/MarlinDev/).
 
 ## Recent Changes
+- RCBugFix
+  - Throw error if compiling with older versions (<1.50) of Arduino due to serios problems with outdated Arduino versions
+  - Please upgrade your IDE.
+
+- RC5 - 01 Apr 2016
+  - Warn if compiling with older versions (<1.50) of Arduino
+  - Fix various LCD menu issues
+  - Add formal support for MKSv1.3 and Sainsmart (RAMPS variants)
+  - Fix bugs in M104, M109, and M190
+  - Fix broken M404 command
+  - Fix issues with M23 and "Start SD Print"
+  - More output for M111
+  - Rename FILAMENT_SENSOR to FILAMENT_WIDTH_SENSOR
+  - Fix SD card bugs
+  - and a lot more
+  - see https://github.com/MarlinFirmware/Marlin/releases/tag/1.1.0-RC5 for details
+
 - RC4 - 24 Mar 2016
   - Many lingering bugs and nagging issues addressed
   - Improvements to LCD menus, CoreXY/CoreXZ, Delta, Bed Leveling, and more…
  - Scott Lahteine [@thinkyhead] - English
  - [@Wurstnase] - Deutsch, English
  - F. Malpartida [@fmalpartida] - English, Spanish
- - [@CONSULitAS] - Deutsch, English
+ - Jochen Groppe [@CONSULitAS] - Deutsch, English
  - [@maverikou]
  - Chris Palmer [@nophead]
  - [@paclema]