Update License Info

Add references to SIMIT, Ligra, and GAPBS,

LICENSE

@@ -1,5 +1,10 @@
 MIT License
 
+Developed by:
+
+  The GraphIt Team
+  https://graphit-lang.org/
+
 Copyright (c) 2018 MIT CSAIL and other contributors
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
@@ -18,4 +23,7 @@ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
+SOFTWARE.
+
+Part of the frontend code was from the SIMIT project (http://simit-lang.org). 
+Part of the runtime libraries were developed based on Ligra and Julienne (https://github.com/jshun/ligra), and GAPBS(https://github.com/sbeamer/gapbs).