Update documentation and change log for cdev feature

Author: almusil

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 - Added serial::Read/Write implementation.
+- Added feature flag for Chardev GPIO
 
 ### Fixed
 
@@ -23,6 +24,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Use embedded-hal::digital::v2 traits.
 - Updated to i2cdev 0.4.3 (necessary for trasactional write-read).
 - Updated to spidev 0.4
+- Added feature flag for Sysfs GPIO
 
 ## [v0.2.2] - 2018-12-21
 

README.md

@@ -13,8 +13,9 @@ This project is developed and maintained by the [Embedded Linux team][team].
 Since Linux kernel v4.4 the use of sysfs GPIO was deprecated and replaced by the character device GPIO.
 See [gpio-cdev documentation](https://github.com/rust-embedded/gpio-cdev#sysfs-gpio-vs-gpio-character-device) for details.
 
-This crate includes feature flag `gpio_cdev` that exposes `CdevPin` as wrapper around `LineHandle` from  [gpio-cdev](https://crates.io/crates/gpio-cdev).
-To enable it update your Cargo.toml. 
+This crate includes feature flag `gpio_cdev` that exposes `CdevPin` as wrapper around `LineHandle` from [gpio-cdev](https://crates.io/crates/gpio-cdev).
+To enable it update your Cargo.toml. Please note that in order to prevent `LineHandle` fd from closing you should
+assign to a variable, see [cdev issue](https://github.com/rust-embedded/gpio-cdev/issues/29) for more details.  
 ```
 linux-embedded-hal = { version = "0.3", features = ["gpio_cdev"] }
 ```