add description and files for local document generation using docker and vscode

Author: haarer

.devcontainer/Dockerfile

@@ -0,0 +1,9 @@
+# Create a Jekyll container for GitHub Pages
+# See this for current supported versions: https://pages.github.com/versions/
+FROM ruby:3.3
+
+# Update the Ruby bundler
+RUN gem update bundler 
+
+# Install Jekyll
+RUN gem install bundler jekyll 

.devcontainer/devcontainer.json

@@ -0,0 +1,8 @@
+// See https://containers.dev/implementors/json_reference/ for configuration reference
+{
+	"name": "SAF Documentation",
+	"dockerFile": "DockerFile",
+    "forwardPorts": [4000, 35729],    
+    "runArgs": ["--name","SAF_docgen_devcontainer"],
+    "postStartCommand": "bundle install && bundle exec jekyll serve --baseurl='' --livereload --force_polling"
+}

src/devdoc/docgen.md

@@ -14,7 +14,27 @@ The SAF Specification is generated into HTML pages from a model. The generation
 ## Github Workflow on SAF Specification Repository
 The SAF Specification repository contains a workflow which generates the HTML pages from the JSON and markdown files. It is triggered by commits to the Specification repository.
 
-## local document generation (setup)
+## Local document generation using docker and vs-code
+ * [install git](https://git-scm.com/downloads)
+ * install wsl 2 (no distro)
+   
+   in a powershell 
+    ```
+    wsl --install --no-distro
+    ```
+ * [install docker desktop](https://docs.docker.com/desktop/setup/install/windows-install/) (a WSL2 based installation)
+ * clone the SAF Specification repository to your machine
+   ```
+   git clone https://github.com/GfSE/SAF-Specification.git
+   ```
+ * [install vs-code](https://code.visualstudio.com/download)
+ * open repo with vs code. Vscode will advise to install some extensions, please follow those recommendations for vscode extensions.
+   Finally this will create the container image and run it.
+   the SAF documentation is available at localhost:4000
+
+## Local document generation (manual setup)
+### setting up local document generation
+ * [install git](https://git-scm.com/downloads)
  * clone the SAF Specification repository to your machine
 
    ```
@@ -28,7 +48,7 @@ The SAF Specification repository contains a workflow which generates the HTML pa
     export PATH="~/.local/share/gem/ruby/3.2.0/bin/:$PATH"
     export BUNDLE_PATH="~/.local/share/gem/ruby/3.2.0/gems/"
     ```
-## local document generation (running)
+### running local document generation
 Run the document generation starting a local web server and open the saf documentation locally
 * in the cloned repository dir, start the generation
   ```