Restore third_party/bazel/README.md in the exported Bazel tree.

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MOS_MIGRATED_REVID=114324917

third_party/protobuf/README.md

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+How to update these files:
+
+1. Go to http://search.maven.org/
+2. Search for g:"com.google.protobuf"
+3. Download the "jar" link from protobuf-java.
+4. Download all binaries from "protoc".
+5. Strip version number from protoc files: for i in *.exe; do mv $i $(echo $i | sed s/3.0.0-alpha-3-//); done
+6. Set executable bit: chmod +x *.exe
+7. Update third_party/BUILD to point to the new jar file.
+8. Done.
+
+
+Because maven.org doesn't have a prebuilt binary for linux on ARM, you need to build the binary
+yourself on the target system. Follow the build steps of protocol buffer to create the binary,
+copy it to this directory and rename it to "protoc-linux-arm32.exe".
+
+For example:
+
+$ cp /usr/bin/protoc $BAZEL/third_party/protobuf/protoc-linux-arm32.exe
+
+This should be done before you run ./compile.sh.
+