Add cd command to FLAC readme. Set executable bit in opus.

Also add jni/flac directory to .gitignore.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=119730955

.gitignore

@@ -41,10 +41,13 @@ proguard-project.txt
 dist
 tmp
 
-# VP9 Extension
+# VP9 extension
 extensions/vp9/src/main/jni/libvpx
 extensions/vp9/src/main/jni/libvpx_android_configs
 extensions/vp9/src/main/jni/libyuv
 
-# Opus Extension
+# Opus extension
 extensions/opus/src/main/jni/libopus
+
+# FLAC extension
+extensions/flac/src/main/jni/flac

extensions/flac/README.md

@@ -35,6 +35,7 @@ NDK_PATH="<path to Android NDK>"
 * Download and extract flac-1.3.1 as "${FLAC_EXT_PATH}/jni/flac" folder:
 
 ```
+cd "${FLAC_EXT_PATH}/jni" && \
 curl http://downloads.xiph.org/releases/flac/flac-1.3.1.tar.xz | tar xJ && \
 mv flac-1.3.1 flac
 ```