starting to define some getting started ReadMe file

GettingStarted.md

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+# GeometryGymIfc toolkit basic principles
+
+# Installation
+
+GeometryGymIfc is available via Nuget. 
+When starting a new project, open the Nuget package manager and search for `GeometryGymIfc`  ([see here](https://www.nuget.org/packages/GeometryGymIFC/))
+
+Installing via package manager console: 
+
+    Install-Package GeometryGymIFC
+
+If a specific version is of interest, add a version flag: 
+
+    Install-Package GeometryGymIFC -Version 0.1.6
+
+Add the reference to your code: 
+
+    using GeometryGym.Ifc;
+
+
+
+# Create, open, and save an Ifc file
+
+## Create new Ifc model
+
+    var database = new DatabaseIfc(ModelView.Ifc4X3_RC2); 
+
+When creating a new database, the user can choose if some boilerplate data should be generated automatically. 
+
+    var database = new DatabaseIfc(true, ModelView.Ifc4X3_RC2). 
+    
+The first argument triggers the boilerplate generation.
+If the constructor is called only be the desired ModelView item, the boilerplate is created by default.
+
+## Open an existing Ifc model
+
+    string path = "<filepath/to/model>";
+    var database = new DatabaseIfc(path);
+
+## Save model in STEP-P21 
+
+    database.WriteFile("myIfcFile.ifc");
+
+<!-- ## Save model in IFCXML
+
+    to be added soon...
+  -->
+<!-- 
+## Setting units in model
+
+### Definition of specific units
+
+    to be added soon... -->
+<!-- 
+### Definition of units using the factory
+
+    to be added soon ...  -->
+
+<!-- 
+## Class constructors
+ 
+
+## out statements in constructors
+
+    to be added soon ... -->
+
+## Database factory
+
+Once the `DatabaseIfc` instance is created, it offers various settings 
+
+### Example 1: Set the application developer: 
+
+    database.Factory.ApplicationDeveloper = "Developer Name";
+
+### Example 2: Set the application name: 
+
+    database.Factory.ApplicationFullName = "IFC Application"; 
+
+### Example 3: Turn off the auto generation of an IfcOwnerHistory: 
+
+    database.Factory.Options.GenerateOwnerHistory = false; 
+
+### Example 4: Add a textual comment in the resulting `*.ifc`  file: 
+
+    var element = new IfcBuiltElement(database);
+    element.AddComment("some comment");
+
+results in 
+
+    /* some comment */
+    #1= IFCBUILTELEMENT('3X4z6TQDjEfweLPwC9InC4',#7,$,$,$,$,$,$);
+
+<!-- ### Example 5: create a fixed guid
+
+Fixing the GUIDs especially is helpful when creating test models. 
+
+    to be added soon ...
+
+## Duplicate factory
+usage: copy concepts from one to another IFC model. 
+
+ -->
+
+# General conventions
+
+## Constructors
+Constructors for IFC classes are typically require all non-optional attributes. 
+Passing `null` into any constructor is typically not intended and leads to non schema compliant IFC files.