Improve building instructions and build error messages

Author: bschwind

README.md

@@ -34,12 +34,14 @@ sudo pacman -S webrtc-audio-processing # Arch
 
 ### Build from source
 
+The webrtc source code is included as a git submodule. Be sure to clone this repo with the `--recursive` flag, or pull the submodule with `git submodule update --init`.
+
 Building from source and static linking can be enabled with the `bundled` feature flag. You need the following tools to build from source:
 
 * `clang` or `gcc`
-* `autotools`
-* `libtoolize` (typically `glibtoolize` on MacOS)
-* `pkg-config`
+* `autotools` (MacOS: `brew install automake`, `brew install autoconf`)
+* `libtoolize` (typically `glibtoolize` on MacOS: `brew install libtool`)
+* `pkg-config` (MacOS: `brew install pkg-config`)
 
 ## Contributing
 

webrtc-audio-processing-sys/build.rs

@@ -111,7 +111,9 @@ mod webrtc {
             command.args(args);
         }
 
-        let _output = command.output()?;
+        let _output = command.output().map_err(|e| {
+            failure::format_err!("Error running command '{}' with args '{:?}' - {:?}", cmd, args_opt, e)
+        })?;
 
         Ok(())
     }