Update readme for JsMaterialX (#1214)

* Update readme for JsMaterialX

source/JsMaterialX/README.md

@@ -34,23 +34,31 @@ The emscripten toolchain is documented [here](https://emscripten.org/docs/buildi
 ### Build
 In the root of directory of this repository run the following:
 
-#### Docker (recommended on Windows machines, not required otherwise)
-It is recommended to build the project with [docker](https://docs.docker.com/) here are the required steps:
+#### Docker
+It is recommended to build the project with Docker, here are the required steps:
+
+  1. Download and install [Docker](https://docs.docker.com/) as instructed on the documentation.
+
+     For Windows make sure to use Linux containers and that File Sharing is set up to allow local directories on Windows to be shared with Linux containers. 
 
-  1. For Windows make sure to use Linux containers and that File Sharing is set up to allow local directories on Windows to be shared with Linux containers. 
-
      For example, if the path to MaterialX is ```"c:\git\MaterialXrepo"``` then the ```"c"``` drive should be set. (See https://docs.docker.com/docker-for-windows/#file-sharing for more details)
 
+     If you work on WSL (Windows Subsystem for Linux), install [Docker](https://docs.docker.com/docker-for-windows/install/) for Windows.
+
   2. Get the `emscripten` docker image
      ```sh
-     docker run -dit --name emscripten -v {path_to_MaterialX}:/src trzeci/emscripten:1.39.7-upstream bash
+     docker run -p 8080:8080 -dit --name emscripten -v {path_to_MaterialX}:/src trzeci/emscripten:1.39.7-upstream bash
      ```
+     For WSL, make sure to run the command on a Windows terminal and also to adjust the path (e.g, `"C:\Users\{windows_username}\AppData\Local\Packages\CanonicalGroupLimited.UbuntuonWindows_{local_code}\LocalState\rootfs\{WSL_path_to_MaterialX}"`).
 
-  3. Build the JavaScript bindings.
+  3. Create a build directory.
+     ```sh
+     docker exec -it emscripten sh -c "[ -d build ] || mkdir build"
+     ``` 
+  4. Build the JavaScript bindings.
      ```sh
      docker exec -it emscripten sh -c "cd build && cmake .. -DMATERIALX_BUILD_JS=ON -DMATERIALX_BUILD_RENDER=OFF -DMATERIALX_BUILD_TESTS=OFF -DMATERIALX_EMSDK_PATH=/emsdk_portable/ && cmake --build . --target install"
      ```
-
 #### CMake
 The JavaScript library can be built using cmake and make.
 
@@ -83,7 +91,7 @@ After building the project the `JsMaterialX.wasm` and `JsMaterialX.js` files can
 ### Install
 To install the results into the test directory run
 ```sh
-cmake --build --target install
+cmake --build . --target install
 ```
 from the build directory.