Update PR templates so users acknowledge they are opening against the right branch.

Author: thewhaleking

.github/PULL_REQUEST_TEMPLATE/bug_fix.md

@@ -56,4 +56,8 @@ Examples:
 - Fixed an issue where multiple cursors did not work in a file with a single line.
 - Increased the performance of searching and replacing across a whole project.
 
--->
+-->
+
+
+### Branch Acknowledgement
+[ ] I am acknowledging that I am opening this branch against `staging`

.github/PULL_REQUEST_TEMPLATE/feature_change.md

@@ -51,4 +51,8 @@ Examples:
 - Fixed an issue where multiple cursors did not work in a file with a single line.
 - Increased the performance of searching and replacing across a whole project.
 
--->
+-->
+
+
+### Branch Acknowledgement
+[ ] I am acknowledging that I am opening this branch against `staging`

.github/PULL_REQUEST_TEMPLATE/performance_improvement.md

@@ -52,4 +52,8 @@ Examples:
 - Fixed an issue where multiple cursors did not work in a file with a single line.
 - Increased the performance of searching and replacing across a whole project.
 
--->
+-->
+
+
+### Branch Acknowledgement
+[ ] I am acknowledging that I am opening this branch against `staging`