docs: update documentation for newly supported targets

Lets get some docs in place about the new Apple and Linux cross
targets that we've recently supported.

Author: indygreg

docs/building.rst

@@ -32,6 +32,15 @@ Building a 32-bit x86 Python distribution is also possible::
 
     $ ./build-linux.py --target i686-unknown-linux-gnu
 
+As are various other targets::
+
+    $ ./build-linux.py --target aarch64-unknown-linux-gnu
+    $ ./build-linux.py --target armv7-unknown-linux-gnueabi
+    $ ./build-linux.py --target armv7-unknown-linux-gnueabihf
+    $ ./build-linux.py --target mips-unknown-linux-gnu
+    $ ./build-linux.py --target mipsel-unknown-linux-gnu
+
+
 macOS
 =====
 

docs/running.rst

@@ -60,7 +60,7 @@ The following shared libraries are referenced:
 * libc.so.6
 * ld-linux-x86-64.so.2
 
-The minimum glibc version required is 2.19. This should make binaries
+The minimum glibc version required is 2.17. This should make binaries
 compatible with the following Linux distributions:
 
 * Fedora 21+

docs/status.rst

@@ -4,18 +4,45 @@
 Project Status
 ==============
 
-There is support for producing 64-bit CPython distributions for Windows,
-macOS, and Linux. All distributions are highly self-contained and have
+There is support for producing CPython distributions for Windows,
+macOS, Linux, and iOS. All distributions are highly self-contained and have
 limited shared library dependencies.
 
 Planned and features include:
 
 * Static/dynamic linking toggles for dependencies
 * Support for configuring which toolchain/version to use
 * Support for BSDs
-* Support for iOS and/or Android
+* Support for Android
 * Support for Python distributions that aren't CPython
 
+Target Notes
+============
+
+Non-Darwin Apple Targets
+------------------------
+
+Apple targets that aren't Darwin/macOS (iOS, tvOS, watchOS, and corresponding
+simulators) are considered alpha quality. The builds may or may not work. The
+builds haven't been widely tested.
+
+Only Python 3.9 is currently supported.
+
+Non-x86 Linux Targets
+---------------------
+
+Linux targets for non-x86 (not ``i686-*`` or ``x86_64-*``) are considered alpha
+quality.
+
+The Linux cross builds use a different build environment based on Debian
+Stretch (as opposed to Debian Jessie) and they use the cross tools Debian
+packages (as opposed to using a modern Clang built from source).
+
+These builds haven't been widely tested. There are likely several rough
+edges with them.
+
+Only Python 3.9 is currently supported.
+
 Test Failures
 =============