Update README.buildsystem.md

Updated SONiC Buildsystem README document by adding pictorial representation of SONiC Build Execution sequence

README.buildsystem.md

@@ -62,6 +62,12 @@ Every **platform/[VENDOR]/** directory is a derived part of buildimage frontend,
 ### Build output
 **target/** is basically a build output. You can find all build artifacts there.  
 
+### SONiC Build Execution sequence
+A pictorial representation depicting the control flow during build execution sequence is shown as below,
+
+![image](https://github.com/thovikeerthi/sonic-buildimage/assets/118048345/78ab5497-434c-4b37-81fb-e6538644f207)
+
+
 ## Recipes and target groups
 Now let's go over a definition of recipes and target groups.  
 **Recipe** is a small makefile that defines a target and set of variables for building it.