docs: changed testing branch to premain

CONTRIBUTING.md

@@ -1 +1 @@
-Please always push on the experimental to ensure we don't mess with the main branch. All the test will be done on the experimental and will be pushed to the main branch after few days of testing.
+Please always push on the premain to ensure we don't mess with the main branch. All the test will be done on the premain and will be pushed to the main branch after few hours or days of testing. and push large or wild changes to experimental so that it can be discussed whether to merge it with main or not in future.