Merge pull request rust-lang#141 from cristianoliveira/patch-1

Adding build note for OS X

README.md

@@ -22,6 +22,27 @@ $ cd git2-rs
 $ cargo build
 ```
 
+## Building on OSX 10.10+
+
+Currently libssh2 requires linking against OpenSSL, and to compile libssh2 it
+also needs to find the OpenSSL headers. On OSX 10.10+ the OpenSSL headers have
+been removed, but if you're using Homebrew you can install them via:
+
+```sh
+brew install openssl
+```
+
+To get this library to pick them up the [standard `rust-openssl`
+instructions][instr] can be used to transitively inform libssh2-sys about where
+the header files are:
+
+[instr]: https://github.com/sfackler/rust-openssl#osx
+
+```sh
+export OPENSSL_INCLUDE_DIR=`brew --prefix openssl`/include
+export OPENSSL_LIB_DIR=`brew --prefix openssl`/lib
+```
+
 # License
 
 `git2-rs` is primarily distributed under the terms of both the MIT license and