added docs that stream must be seekable for StageBlock (Azure#48515)

Author: nickliu-msft

sdk/storage/Azure.Storage.Blobs/src/BlockBlobClient.cs

@@ -996,6 +996,7 @@ internal virtual async Task<Response<BlobContentInfo>> UploadInternal(
         /// </param>
         /// <param name="content">
         /// A <see cref="Stream"/> containing the content to upload.
+        /// The <see cref="Stream"/> must be seekable.
         /// </param>
         /// <param name="transactionalContentHash">
         /// An optional MD5 hash of the block <paramref name="content"/>.
@@ -1068,6 +1069,7 @@ public virtual Response<BlockInfo> StageBlock(
         /// </param>
         /// <param name="content">
         /// A <see cref="Stream"/> containing the content to upload.
+        /// The <see cref="Stream"/> must be seekable.
         /// </param>
         /// <param name="transactionalContentHash">
         /// An optional MD5 hash of the block <paramref name="content"/>.
@@ -1140,6 +1142,7 @@ public virtual async Task<Response<BlockInfo>> StageBlockAsync(
         /// </param>
         /// <param name="content">
         /// A <see cref="Stream"/> containing the content to upload.
+        /// The <see cref="Stream"/> must be seekable.
         /// </param>
         /// <param name="options">
         /// Optional parameters.
@@ -1191,6 +1194,7 @@ public virtual Response<BlockInfo> StageBlock(
         /// </param>
         /// <param name="content">
         /// A <see cref="Stream"/> containing the content to upload.
+        /// The <see cref="Stream"/> must be seekable.
         /// </param>
         /// <param name="options">
         /// Optional parameters.
@@ -1242,6 +1246,7 @@ await StageBlockInternal(
         /// </param>
         /// <param name="content">
         /// A <see cref="Stream"/> containing the content to upload.
+        /// The <see cref="Stream"/> must be seekable.
         /// </param>
         /// <param name="conditions">
         /// Access conditions for staging the block.