Improve end-of-stream handling. (#255)

* Improve end-of-stream handling.

As discussed in issue #247.

* Update docs/essentials/index.md.

Improve wording.

Co-authored-by: Maxim Schuwalow <16665913+mschuwalow@users.noreply.github.com>

* Update for latest master.

Co-authored-by: Maxim Schuwalow <16665913+mschuwalow@users.noreply.github.com>
Co-authored-by: Jakub Czuchnowski <jakub.czuchnowski@gmail.com>

docs/essentials/index.md

@@ -59,6 +59,26 @@ val read100: ZIO[Blocking, Option[IOException], Chunk[Byte]] =
 
 End-of-stream will be signalled with `None`. Any errors will be wrapped in `Some`.
 
+### End-Of-Stream Handling
+
+When reading from channels, the end of the stream may be reached at any time. This is indicated by the read effect failing with an `java.io.EOFException`. If you would prefer to explicitly represent the end-of-stream condition in the error channel, use the `eofCheck` extension method:
+
+```scala mdoc:silent
+import zio._
+import zio.blocking.Blocking
+import zio.nio._
+import zio.nio.channels._
+import zio.nio.file.Path
+import java.io.IOException
+
+val read100: ZIO[Blocking, Option[IOException], Chunk[Byte]] =
+  FileChannel.open(Path("foo.txt"))
+    .asSomeError
+    .use(_.readChunk(100).eofCheck)
+```
+
+End-of-stream will be signalled with `None`. Any errors will be wrapped in `Some`.
+
 ## References
 
  - [ZIO github page](http://github.com/zio/zio)