Import SIMD feature and add some workload samples (#438)

samples/workload/bwa/README.md

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+"bwa" sample introduction
+==============
+
+This sample demonstrates how to build [bwa](https://github.com/lh3/bwa) into
+WebAssembly with simd support and run it with iwasm.
+
+## Preparation
+
+please refer to [installation instructions](../README.md).
+
+## Build
+
+``` shell
+$ mkdir build && cd build
+$ cmake ..
+$ make
+# to verify
+$ ls bwa.wasm
+```
+
+## Download sample data
+
+Download the bwa-0.7.15 binary package from
+[such an address](https://sourceforge.net/projects/bio-bwa/files/bwakit/bwakit-0.7.15_x64-linux.tar.bz2/download),
+a sample data file named **hs38DH.fa** will be used later.
+
+If want more data, please refer to http://hgdownload.cse.ucsc.edu/goldenpath/hg19/bigZips/
+
+## Run workload
+
+Firstly please build iwasm with simd support:
+
+``` shell
+$ cd <wamr dir>/product-mini/platforms/linux/
+$ mkdir build && cd build
+$ cmake .. -DWAMR_BUILD_SIMD=1
+$ make
+```
+
+Then compile wasm file to aot file and run:
+
+``` shell
+$ cd <wamr dir>/wamr-compiler/build
+$ ./wamrc --enable-simd -o bwa.aot ./bwa.wasm
+$ cd <wamr dir>/product-mini/platforms/linux/
+$ ./iwasm --dir=. ./bwa.aot index hs38DH.fa
+```