feat: new FindPython support (#2370)

* feat: FindPython support

* refactor: rename to PYBIND11_FINDPYTHON

* docs: Caps fixes

* feat: NOPYTHON mode

* test: check simple call

* docs: add changelog/upgrade guide

* feat: Support Python3 and Python2

* refactor: Use targets in tests

* fix: support CMake 3.4+

* feat: classic search also finds virtual environments

* docs: some updates from @wjakob's review

* fix: wrong name for QUIET mode variable, reported by @skoslowski

* refactor: cleaner output messaging

* fix: support debug Python's in FindPython mode too

* fixup! refactor: cleaner output messaging

* fix: missing pybind11_FOUND and pybind11_INCLUDE_DIR restored to subdir mode

* fix: nicer reporting of Python / PyPy

* fix: out-of-order variable fix

* docs: minor last-minute cleanup
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 2def2b0..fbb3667 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -6,6 +6,39 @@
 Starting with version 1.8.0, pybind11 releases use a `semantic versioning
 <http://semver.org>`_ policy.
 
+v2.6.0 (IN PROGRESS)
+--------------------
+
+See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
+
+* Minimum CMake required increased to 3.4.
+  `#2338 <https://github.com/pybind/pybind11/pull/2338>`_ and
+  `#2370 <https://github.com/pybind/pybind11/pull/2370>`_
+
+  * Full integration with CMake’s C++ standard system replaces
+    ``PYBIND11_CPP_STANDARD``.
+
+  * Generated config file is now portable to different Python/compiler/CMake
+    versions.
+
+  * Virtual environments prioritized if ``PYTHON_EXECUTABLE`` is not set
+    (``venv``, ``virtualenv``, and ``conda``) (similar to the new FindPython
+    mode).
+
+  * Other CMake features now natively supported, like
+    ``CMAKE_INTERPROCEDURAL_OPTIMIZATION``, ``set(CMAKE_CXX_VISIBILITY_PRESET
+    hidden)``.
+
+* Optional :ref:`find-python-mode` and :ref:`nopython-mode` with CMake.
+  `#2370 <https://github.com/pybind/pybind11/pull/2370>`_
+
+* Uninstall target added.
+  `#2265 <https://github.com/pybind/pybind11/pull/2265>`_ and
+  `#2346 <https://github.com/pybind/pybind11/pull/2346>`_
+
+
+
+
 v2.5.0 (Mar 31, 2020)
 -----------------------------------------------------