Merge pull request #175 from zpg6/docs/writing-to-files-snippet-for-crate-doc

docs: adds same snippet of writing to files to `lib.rs` for crate doc

Author: thejpster

src/lib.rs

@@ -43,6 +43,25 @@
 //! }
 //! ```
 //!
+//! For writing files:
+//!
+//! ```rust
+//! use embedded_sdmmc::{BlockDevice, Directory, Error, Mode, TimeSource};
+//! fn write_file<D: BlockDevice, T: TimeSource, const DIRS: usize, const FILES: usize, const VOLUMES: usize>(
+//!     root_dir: &mut Directory<D, T, DIRS, FILES, VOLUMES>,
+//! ) -> Result<(), Error<D::Error>>
+//! {
+//!     let my_other_file = root_dir.open_file_in_dir("MY_DATA.CSV", Mode::ReadWriteCreateOrAppend)?;
+//!     my_other_file.write(b"Timestamp,Signal,Value\n")?;
+//!     my_other_file.write(b"2025-01-01T00:00:00Z,TEMP,25.0\n")?;
+//!     my_other_file.write(b"2025-01-01T00:00:01Z,TEMP,25.1\n")?;
+//!     my_other_file.write(b"2025-01-01T00:00:02Z,TEMP,25.2\n")?;
+//!     // Don't forget to flush the file so that the directory entry is updated
+//!     my_other_file.flush()?;
+//!     Ok(())
+//! }
+//! ```
+//!
 //! ## Features
 //!
 //! * `log`: Enabled by default. Generates log messages using the `log` crate.