Added details for platform/build requirements.

Also added Qt version check.
And made the platform/toolchain check a little more descriptive.

README.md

@@ -56,7 +56,15 @@ QGroundControl can talk to XBee wireless devices using their proprietary protoco
 
 To disable XBee support you may add `DISABLE_XBEE` to the DEFINES argument.
 
-# Build on Mac OSX
+## Building QGroundControl
+
+### Requirements
+QGroundControl requires Qt5.2+ and SDL1.2 at a minimum. Additionally, only the following platform targets are supported:
+  * Windows: Microsoft Visual Studio 2010, 2012, 2013
+  * Linux: gcc, 32- or 64-bit
+  * Mac: LLVM+clang 64-bit
+
+## Build on Mac OSX
 
 To build on Mac OSX (10.6 or later):
 - - -
@@ -79,7 +87,7 @@ To build on Mac OSX (10.6 or later):
 3. Run `make -j4`
 
 
-# Build on Linux
+## Build on Linux
 
 To build on Linux:
 - - -
@@ -120,7 +128,7 @@ To build on Linux:
 6. Run qgroundcontrol
   1. `./release/qgroundcontrol`
 
-# Build on Windows
+## Build on Windows
 - - -
 
 Only compilation using Visual Studio 2010, 2012, and 2013 are supported.

qgroundcontrol.pro

@@ -23,17 +23,33 @@ message(Qt version $$[QT_VERSION])
 # to allow us to easily modify suported build types in one place instead of duplicated throughout
 # the project file.
 
-linux-g++ | linux-g++-64 {
-    message(Linux build)
-    CONFIG += LinuxBuild
-} else : win32-msvc2008 | win32-msvc2010 | win32-msvc2012 | win32-msvc2013 {
-    message(Windows build)
-    CONFIG += WindowsBuild
-} else : macx-clang | macx-llvm {
-    message(Mac build)
-    CONFIG += MacBuild
+!equals(QT_MAJOR_VERSION, 5) | !greaterThan(QT_MINOR_VERSION, 1) {
+    error("Unsupported Qt version, 5.2+ is required")
+}
+
+linux {
+    linux-g++ | linux-g++-64 {
+        message("Linux build")
+        CONFIG += LinuxBuild
+    } else {
+        message("Unsuported Linux toolchain, only GCC 32- or 64-bit is supported")
+    }
+} else : win32 {
+    win32-msvc2010 | win32-msvc2012 | win32-msvc2013 {
+        message("Windows build")
+        CONFIG += WindowsBuild
+    } else {
+        message("Unsupported Windows toolchain, only Visual Studio 2010, 2012, and 2013 are supported")
+    }
+} else : macx {
+    macx-clang | macx-llvm {
+        message("Mac build")
+        CONFIG += MacBuild
+    } else {
+        message("Unsupported Mac toolchain, only 64-bit LLVM+clang is supported")
+    }
 } else {
-    error(Unsupported build type)
+    error("Unsupported build platform, only Linux, Windows, and Mac are supported")
 }
 
 # Installer configuration