Fix Docker pack: copy README and .git for packaging and Source Link

The pack stage failed with NU5019 (File not found: '/README.md') because
the new PackageReadmeFile content was never copied into the build context.
Copy README.md alongside icon.png.

Also copy ./.git (and stop ignoring it) so Microsoft.SourceLink.GitHub can
resolve the commit and emit real source link information instead of warning
that source control information is unavailable.

Author: kevbite

.dockerignore

@@ -1,5 +1,4 @@
 **/bin
 **/obj
 **/.vscode
-**/.vs
-.git
+**/.vs

Dockerfile

@@ -13,7 +13,9 @@ RUN dotnet restore
 
 FROM restore AS build
 ARG VERSION
+COPY ./.git ./.git
 COPY ./icon.png .
+COPY ./README.md .
 COPY ./src/Kevsoft.WLED/ ./src/Kevsoft.WLED/
 COPY ./src/Kevsoft.WLED.DependencyInjection/ ./src/Kevsoft.WLED.DependencyInjection/
 RUN dotnet build ./src/Kevsoft.WLED.DependencyInjection/Kevsoft.WLED.DependencyInjection.csproj --configuration Release -p:Version=${VERSION} --no-restore