Update Readme with more detail for OS X build

Mac-compatibility-build.md

@@ -0,0 +1,25 @@
+# Building On OSX for maximum compatibility
+
+## Install Older Platform SDKs
+Use [this script](http://devernay.free.fr/hacks/xcodelegacy/) to install older SDKs.
+
+## Additional configure flags for compiling wxWidgets
+### Building on 10.8 or newer
+* --with-macosx-version-min=10.5 
+* --with-macosx-sdk=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.5.sdk
+
+### Building on 10.5 to 10.7
+* --with-macosx-version-min=10.5
+* --with-macosx-sdk=/Developer/SDKs/MacOSX10.5.sdk
+
+
+## Recommended flags for development/debugging (Assuming OS X > 10.7)
+* --enable-debug_gdb
+* --enable-profile
+* --enable-arttango
+* --disable-compat28
+* --disable-shared
+* --without-webviewwebkit
+* --with-macosx-version-min=10.5
+* --with-macosx-sdk=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.5.sdk
+

README.md

@@ -29,6 +29,10 @@ After these packages are installed, the project should build with a simple `make
 ### OS X
 Building wxWidgets:
 
+If you want maximum compatibility with older versions of OS X, 
+view [the guide](./Mac-compatibility-build.md). Otherwise, these simpler 
+steps should work fine for a local build.
+
 1. Download the latest wxWidgets source
 2. Make a new directory in the source tree, like `wxmac`
 3. Run `../configure --disable-shared --disable-webviewwebkit` in the new directory