Use <GUID> property if present for BepInExPluginGuid (#20)

* Use <GUID> property if present for BepInExPluginGuid

* Add GUID tag info to PluginInfoProps readme

---------

Co-authored-by: 10_days_till_xmas <x10-days-till-xmas@outlook.com>
Co-authored-by: ManlyMarco <39247311+ManlyMarco@users.noreply.github.com>

Author: 3 people

BepInEx.PluginInfoProps/BepInEx.PluginInfoProps.props

@@ -1,6 +1,7 @@
 <Project>
     <Target Name="AddGeneratedFile" BeforeTargets="BeforeCompile;CoreCompile" Inputs="$(MSBuildAllProjects)" Outputs="$(IntermediateOutputPath)GeneratedFile.cs">
         <PropertyGroup>
+            <BepInExPluginGuid Condition="'$(BepInExPluginGuid)' == ''">$(GUID)</BepInExPluginGuid>
             <BepInExPluginGuid Condition="'$(BepInExPluginGuid)' == ''">$(AssemblyName)</BepInExPluginGuid>
             <BepInExPluginName Condition="'$(BepInExPluginName)' == ''">$(Product)</BepInExPluginName>
             <BepInExPluginVersion Condition="'$(BepInExPluginVersion)' == ''">$(Version)</BepInExPluginVersion>

BepInEx.PluginInfoProps/README.md

@@ -7,7 +7,7 @@ Generates `MyPluginInfo.cs` based on csproj tags.
 Define the following properties in your `csproj`:
 
 ```xml
-<AssemblyName>Example.Plugin</AssemblyName>
+<GUID>Example.Plugin</GUID> <!--  Optional. If missing, <AssemblyName> is used as GUID instead. -->
 <Product>My first plugin</Product>
 <Version>1.0.0</Version>
 ```