chore: fix nuget package README.md path (?)

Author: pmiossec

src/GitExtensions.AzureDevOpsCommitMessage/GitExtensions.AzureDevOpsCommitMessage.nuspec

@@ -7,7 +7,7 @@
     <description>$description$</description>
     <projectUrl>$projectUrl$</projectUrl>
     <icon>Resources\IconAzureDevOps.png</icon>
-    <readme>readme.md</readme>
+    <readme>README.md</readme>
     <tags>$tags$</tags>
     <dependencies>
       <dependency id="GitExtensions.Extensibility" version="[0.1.0, 1.0.0)" />