docs: Update zip_writer documentation example (#431)

* Update zip_writer documentation example

Replace the fixed size buffer example with a dynamic Vec

Since the buffer size was of fixed, size, the resulting zip file was always the
same size, defeating the purpose of compression

* Comment inside an example needs "/// //"

Signed-off-by: Chris Hennick <[email protected]>

---------

Signed-off-by: Chris Hennick <[email protected]>
Co-authored-by: Chris Hennick <[email protected]>

Author: romuald

src/write.rs

@@ -143,9 +143,9 @@ pub(crate) mod zip_writer {
     /// use std::io::Write;
     /// use zip::write::SimpleFileOptions;
     ///
-    /// // We use a buffer here, though you'd normally use a `File`
-    /// let mut buf = [0; 65536];
-    /// let mut zip = ZipWriter::new(std::io::Cursor::new(&mut buf[..]));
+    /// // We use a cursor + vec here, though you'd normally use a `File`
+    /// let mut cur = std::io::Cursor::new(Vec::new());
+    /// let mut zip = ZipWriter::new(&mut cur);
     ///
     /// let options = SimpleFileOptions::default().compression_method(zip::CompressionMethod::Stored);
     /// zip.start_file("hello_world.txt", options)?;
@@ -155,6 +155,9 @@ pub(crate) mod zip_writer {
     /// // Dropping the `ZipWriter` will have the same effect, but may silently fail
     /// zip.finish()?;
     ///
+    /// // raw zip data is available as a Vec<u8>
+    /// let zip_bytes = cur.into_inner();
+    ///
     /// # Ok(())
     /// # }
     /// # doit().unwrap();