Include XML documentation file in NuGet package

Enable GenerateDocumentationFile in the Editor csproj so the XML doc
file ships alongside the DLL in lib/net10.0/. This allows DocFX and
other documentation tools to extract API summaries from the package.

Suppress CS1574/CS1591/CS1723 doc-comment warnings that surface from
lifted AvaloniaEdit code and cross-assembly cref references.

Add API documentation link to README.md.

Closes #222

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: tig

README.md

@@ -4,7 +4,7 @@
 
 A reusable text-editing `View` for [Terminal.Gui](https://github.com/gui-cs/Terminal.Gui). Drop it into your TUI app and you get the editing experience users already expect (caret movement, selection, clipboard, undo/redo, search & replace, folding, syntax highlighting, word wrap) without writing any of it yourself.
 
-Ships as a single NuGet package: **[`Terminal.Gui.Editor`](https://www.nuget.org/packages/Terminal.Gui.Editor)**.
+Ships as a single NuGet package: **[`Terminal.Gui.Editor`](https://www.nuget.org/packages/Terminal.Gui.Editor)**. API documentation is published on the [Terminal.Gui DocFX site](https://gui-cs.github.io/Terminal.Gui/api/Terminal.Gui.Editor.html).
 
 ## What this is, and what it isn't
 

src/Terminal.Gui.Editor/Terminal.Gui.Editor.csproj

@@ -3,6 +3,11 @@
   <PropertyGroup>
     <RootNamespace>Terminal.Gui.Editor</RootNamespace>
     <AssemblyName>Terminal.Gui.Editor</AssemblyName>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <!-- CS1574: XML comment has cref that could not be resolved (cross-assembly refs to Terminal.Gui internals).
+         CS1591: Missing XML comment for publicly visible type/member (lifted AvaloniaEdit code lacks full docs).
+         CS1723: XML comment has cref that refers to a type parameter (upstream doc style). -->
+    <NoWarn>$(NoWarn);CS1574;CS1591;CS1723</NoWarn>
 
     <PackageId>Terminal.Gui.Editor</PackageId>
     <Description>Full-featured text editor View for Terminal.Gui — rope-backed document model, multi-caret, folding, search, undo/redo, optional TextMate highlighting. Adapted from AvaloniaEdit.</Description>