Start RELEASE_NOTES.md and CHANGES.md sections for new release

CHANGES.md

@@ -12,6 +12,16 @@ Note that users who upgrade the simulator across versions, or who work directly
 
 This file is a best-effort approach to solving this issue; we will do our best but can guarantee that there will be things that fall through the cracks, unfortunately. If you, as a user, can suggest improvements to this file based on your experience, please contribute a patch or drop us a note on ns-developers mailing list.
 
+## Changes from ns-3.46 to ns-3-dev
+
+### New API
+
+### Changes to existing API
+
+### Changes to build system
+
+### Changed behavior
+
 ## Changes from ns-3.45 to ns-3.46
 
 ### New API

RELEASE_NOTES.md

@@ -12,6 +12,32 @@ a [GitLab.com issue tracker](https://gitlab.com/nsnam/ns-3-dev/-/issues) number,
 and references prefixed by '!' refer to a
 [GitLab.com merge request](https://gitlab.com/nsnam/ns-3-dev/-/merge_requests) number.
 
+## Release 3-dev
+
+### Supported platforms
+
+This release is intended to work on systems with the following minimal
+requirements (Note: not all ns-3 features are available on all systems):
+
+- g++-11.1 or later, or LLVM/clang++-17 or later
+- Python 3.8 or later
+- CMake 3.20 or later
+- (macOS only) Xcode 16.2 or later
+- (Windows only) Msys2/MinGW64, Msys2/UCRT64 and ClangCL/MSVC toolchains, or WSL2
+
+The version of clang-format enforced by the check-style-clang-format.py script for
+this release is version 20 only.
+
+Version 20 of the clang-tidy linter is now supported and recommended, although versions 15-19
+are still compatible.
+
+Python API requires [Cppyy](https://cppyy.readthedocs.io/en/latest/installation.html) and has only
+been tested on Linux. As of this release, the latest known version to work with ns-3 is cppyy==3.5.0.
+
+### New user-visible features
+
+### Bugs fixed
+
 ## Release 3.46
 
 This release is available from: