Simplify VSIX process

Author: AArnott

doc/vsix.md

@@ -8,6 +8,4 @@ the version calculated from your version.json file and git height.
 1. Install the Nerdbank.GitVersioning NuGet package into your VSIX-generating project.
 1. Open the `source.extension.vsixmanifest` file in a code editor
 and set the `PackageManifest/Metadata/Identity/@Version` attribute to this
-value: `|YourProjectName;GetBuildVersion|` where `YourProjectName` is
-obviously replaced with the actual project name (without extension) of your
-VSIX project.
+value: `|%CurrentProject%;GetBuildVersion|`