Correct spelling mistakes in doc folder

- OSX —> OS X
- XCode —> Xcode
- github —> GitHub
- homebrew —> Homebrew
- gitian —> Gitian
- Other miscellaneous obvious spelling fixes and whitespace removal

doc/README.md

@@ -7,7 +7,7 @@ Setup
 
 Running
 ---------------------
-The following are some helpful notes on how to run Bitcoin on your native platform. 
+The following are some helpful notes on how to run Bitcoin on your native platform.
 
 ### Unix
 
@@ -26,7 +26,7 @@ Unpack the files into a directory and run:
 
 Unpack the files into a directory, and then run bitcoin-qt.exe.
 
-### OSX
+### OS X
 
 Drag Bitcoin-Qt to your applications folder, and then run Bitcoin-Qt.
 
@@ -41,7 +41,7 @@ Building
 ---------------------
 The following are developer notes on how to build Bitcoin on your native platform. They are not complete guides, but include notes on the necessary libraries, compile flags, etc.
 
-- [OSX Build Notes](build-osx.md)
+- [OS X Build Notes](build-osx.md)
 - [Unix Build Notes](build-unix.md)
 - [Gitian Building Guide](gitian-building.md)