Update image download url (#24485)

Why I did it
Update image download url, the old url is deprecated.

signed-off-by: [email protected]

Author: yejianquan

README.md

@@ -51,7 +51,7 @@
 
 ## SONiC Image Azure Pipelines
 
-All SONiC project build pipeline could be found at [Download Portal for SONiC Images](https://sonic-build.azurewebsites.net)
+All SONiC project build pipelines can be found at [Download Portal for SONiC Images](https://sonic-build.azurewebsites.net/pipelines)
 
 # sonic-buildimage