Update UMass OS

README.md

@@ -191,6 +191,7 @@ Table of Contents
   - [CS 4414 Operating Systems, Fall 2018 - University of Virginia](https://www.cs.virginia.edu/~cr4bd/4414/F2018/schedule.html)
   - [CSE 421/521 - Introduction to Operating Systems, SUNY University at Buffalo, NY - Spring 2016](https://www.ops-class.org/courses/buffalo/CSE421_Spring2016/) ([Lectures - YouTube](https://www.youtube.com/playlist?list=PLE6LEE8y2Jp-kbEcVR2W3vfx0Pdca0BD3)) ([Recitations 2016](https://www.youtube.com/playlist?list=PLE6LEE8y2Jp_YJn8wu9aJTPOgeWqiaJDF)) ([Assignment walkthroughs](https://www.youtube.com/playlist?list=PLE6LEE8y2Jp9PC8fyzc2meL4XvrVSyP8O))
   - [CS 377 - Operating Systems, Fall 16 - Umass OS](https://www.youtube.com/playlist?list=PLacuG5pysFbDTmsCRGWsMW_PzIOpXnckw)
+  - [CS 577 - Operating Systems, Spring 20 - Umass OS](https://www.youtube.com/playlist?list=PLacuG5pysFbB2_z9EkSfQIjq3yNzy8igs)
   - [6.828 - Operating System Engineering [Fall 2014]](https://www.youtube.com/playlist?list=PLfciLKR3SgqNJKKIKUliWoNBBH1VHL3AP)
   - [6.S081 - Operating System Engineering [Fall 2020]](https://pdos.csail.mit.edu/6.828/2020/schedule.html)
   - [CSE 30341 - Operating Systems, Spr 2008](https://www.youtube.com/view_play_list?p=AB7D5CA7E262B0E2)
@@ -200,7 +201,7 @@ Table of Contents
   - [CSE 60641 - Graduate Operating Systems, Fall 08](https://www.youtube.com/view_play_list?p=22B10D854588E20C)
   - [Advanced Programming in the UNIX Environment](https://stevens.netmeister.org/631/)
 - #### **Distributed Systems**
-  - [CS 677 - Distributed Operating Systems, Spring 16 - Umass OS](https://www.youtube.com/playlist?list=PLacuG5pysFbC68w0PW3huMHDDRNsDCTjp)
+  - [CS 677 - Distributed Operating Systems, Spring 24 - Umass OS](https://www.youtube.com/playlist?list=PLacuG5pysFbBpWHfKUU9Dfdk8RmQ7B9EH)
   - [CS 436 - Distributed Computer Systems - U Waterloo](https://www.youtube.com/playlist?list=PLawkBQ15NDEkDJ5IyLIJUTZ1rRM9YQq6N)
   - [6.824 - Distributed Systems, Spring 2015 - MIT](https://www.youtube.com/playlist?list=PLkcQbKbegkMqiWf7nF8apfMRL4P4sw8UL)
   - [6.824 Distributed Systems - Spring 2020 - MIT](https://pdos.csail.mit.edu/6.824/schedule.html) ([Youtube](https://www.youtube.com/playlist?list=PLrw6a1wE39_tb2fErI4-WkMbsvGQk9_UB))