LICENSE: Reference third-party licenses.

This is to provide a summary of the licenses used by MicroPython.

- Add SPDX identifier for every directory that includes
  non-MIT-licensed content.
- Add brief summary.
- Update docs license to be more explicit.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

LICENSE

@@ -19,3 +19,68 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
+
+--------------------------------------------------------------------------------
+
+Unless specified otherwise (see below), the above license and copyright applies
+to all files in this repository.
+
+Individual files may include additional copyright holders.
+
+The various ports of MicroPython may include third-party software that is
+licensed under different terms. These licenses are summarised in the tree
+below, please refer to these files and directories for further license and
+copyright information. Note that (L)GPL-licensed code listed below is only
+used during the build process and is not part of the compiled source code.
+
+/ (MIT)
+    /drivers
+        /cc3000 (BSD-3-clause)
+        /cc3100 (BSD-3-clause)
+        /wiznet5k (BSD-3-clause)
+    /extmod
+        /crypto-algorithms (NONE)
+        /re15 (BSD-3-clause)
+        /uzlib (Zlib)
+    /lib
+        /asf4 (Apache-2.0)
+        /axtls (BSD-3-clause)
+            /config
+                /scripts
+                    /config (GPL-2.0-or-later)
+                /Rules.mak (GPL-2.0)
+        /berkeley-db-1xx (BSD-4-clause)
+        /btstack (See btstack/LICENSE)
+        /cmsis (BSD-3-clause)
+        /libhydrogen (ISC)
+        /littlefs (BSD-3-clause)
+        /lwip (BSD-3-clause)
+        /mynewt-nimble (Apache-2.0)
+        /nrfx (BSD-3-clause)
+        /nxp_driver (BSD-3-Clause)
+        /oofatfs (BSD-1-clause)
+        /pico-sdk (BSD-3-clause)
+        /stm32lib (BSD-3-clause)
+        /tinytest (BSD-3-clause)
+        /tinyusb (MIT)
+    /logo (uses OFL-1.1)
+    /ports
+        /cc3200
+            /hal (BSD-3-clause)
+            /simplelink (BSD-3-clause)
+            /FreeRTOS (GPL-2.0 with FreeRTOS exception)
+        /stm32
+            /usbd*.c (MCD-ST Liberty SW License Agreement V2)
+            /stm32_it.* (MIT + BSD-3-clause)
+            /system_stm32*.c (MIT + BSD-3-clause)
+            /boards
+                /startup_stm32*.s (BSD-3-clause)
+                /*/stm32*.h (BSD-3-clause)
+            /usbdev (MCD-ST Liberty SW License Agreement V2)
+            /usbhost (MCD-ST Liberty SW License Agreement V2)
+        /teensy
+            /core (PJRC.COM)
+        /zephyr
+            /src (Apache-2.0)
+    /tools
+        /dfu.py (LGPL-3.0-only)

docs/conf.py

@@ -66,7 +66,7 @@ master_doc = 'index'
 
 # General information about the project.
 project = 'MicroPython'
-copyright = '2014-2021, Damien P. George, Paul Sokolovsky, and contributors'
+copyright = '- The MicroPython Documentation is Copyright © 2014-2021, Damien P. George, Paul Sokolovsky, and contributors'
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the