Update licensing information for SurfSense software

- Added Business Source License 1.1 details to the proprietary LICENSE file.
- Clarified terms of use, including production use restrictions and transition to Apache License after four years.
- Updated README.md to reflect the new licensing structure and its implications for users.

This change ensures clear communication of licensing terms for proprietary components within the SurfSense project.

LICENSE

@@ -1,3 +1,18 @@
+Copyright (c) SurfSense
+
+Portions of this software are licensed as follows:
+
+* All content that resides under the "surfsense_backend/app/proprietary/"
+  directory of this repository is licensed under the Business Source License
+  1.1 as defined in "surfsense_backend/app/proprietary/LICENSE".
+* All third-party components incorporated into the SurfSense software are
+  licensed under the original license provided by the owner of the applicable
+  component.
+* Content outside of the above-mentioned directory is available under the
+  Apache License, Version 2.0, as defined below.
+
+-----------------------------------------------------------------------------
+
                                  Apache License
                            Version 2.0, January 2004
                         http://www.apache.org/licenses/