Added documentation.

src/Skia/Avalonia.Skia/SKPaintCache.cs

@@ -1,13 +1,11 @@
-using System;
-using System.Collections.Concurrent;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
+using System.Collections.Concurrent;
 using SkiaSharp;
 
 namespace Avalonia.Skia
 {
+    /// <summary>
+    /// Cache for SKPaints.
+    /// </summary>
     internal static class SKPaintCache
     {
         private static ConcurrentBag<SKPaint> s_cachedPaints;
@@ -17,6 +15,14 @@ namespace Avalonia.Skia
             s_cachedPaints = new ConcurrentBag<SKPaint>();
         }
 
+        /// <summary>
+        /// Gets a SKPaint for usage.
+        /// </summary>
+        /// <remarks>
+        /// If a SKPaint is in the cache, that existing SKPaint will be returned.
+        /// Otherwise a new SKPaint will be created.
+        /// </remarks>
+        /// <returns></returns>
         public static SKPaint Get()
         {
             if (!s_cachedPaints.TryTake(out var paint))
@@ -27,12 +33,24 @@ namespace Avalonia.Skia
             return paint;
         }
 
+        /// <summary>
+        /// Returns a SKPaint for reuse later.
+        /// </summary>
+        /// <remarks>
+        /// Do not use the paint further.
+        /// Do not return the same paint multiple times as that will break the cache.
+        /// Uses SKPaint.Reset() for reuse later.
+        /// </remarks>
+        /// <param name="paint"></param>
         public static void Return(SKPaint paint)
         {
             paint.Reset();
             s_cachedPaints.Add(paint);
         }
 
+        /// <summary>
+        /// Clears and disposes all cached paints.
+        /// </summary>
         public static void Clear()
         {
             while (s_cachedPaints.TryTake(out var paint))