[DOCS] Neural network Deployment Guide with System Module Mode #1523 (#1533)

docs/deploy/nnvm.md

@@ -116,3 +116,60 @@ int main()
     return 0;
 }
 ```
+
+## Deploy as System Module
+C++ additionally support deployment as system module.
+This process need few additional options as given below to NNVM build.
+
+- For target llvm append --system-lib as ```target=llvm --system-lib```
+- For a GPU build (or non llvm) the additional option should be given to targat_host as ```target_host=llvm --system-lib```
+
+Module export require additional options for not to compile but save as ```lib.export_library (path, fcompile=False)```
+
+The output of above API is a tar compressed file containing object file ```(lib.o)``` and cpp source file ```(devc.cc)``` which embeds device blob. Thease two files should be compiled along with other files or objects while building c++ application.
+Please refer to [Makefile](https://github.com/dmlc/tvm/tree/master/apps/howto_deploy/Makefile#L32) for a reference.
+
+The c++ code to load this system module require the below change.
+
+```cpp
+    // tvm module for compiled functions
+    tvm::runtime::Module mod_syslib = (*tvm::runtime::Registry::Get("module._GetSystemLib"))();
+```
+
+Based on the build environment the system object, device blob source should be included in the final executable. An example with bazel build is given below.
+```bash
+cc_library(
+    name = "host_module",
+    srcs = ["lib.o"],
+    alwayslink=1
+)
+
+cc_library(
+    name = "device_module",
+    srcs = ["devc.cc"],
+    alwayslink=1
+)
+
+cc_library(
+    name = "tvm_runtime",
+    srcs = ["libtvm_runtime_pack.cc"],
+)
+
+cc_binary(
+    name = "bazel_deploy",
+    srcs = ["cpp_deploy.cc"],
+    deps = [
+        ":tvm_runtime", ":host_module", ":device_module"
+    ],
+    linkopts = [ "-lpthread -ldl" ]
+)
+
+```
+
+This build directive creates
+- new library ```host_module``` out of ```lib.o```
+- new library ```device_module``` out of ```devc.cc```
+
+These intermediate modules can be used as a dependency to final deploy application.
+
+In bazel ```alwayslink=1``` enforce embedding entire lib into application (even though it doesn't call any API from this module).