Added hostname parameter

README.md

@@ -62,7 +62,7 @@ The following environment variables are supported:
    be built and cached.  Note, `WORK_DIR` stores a complete copy of the target
    system for each build stage, amounting to tens of gigabytes in the case of
    Raspbian.
-   
+
    **CAUTION**: If your working directory is on an NTFS partition you probably won't be able to build. Make sure this is a proper Linux filesystem.
 
  * `DEPLOY_DIR`  (Default: `"$BASE_DIR/deploy"`)
@@ -82,6 +82,10 @@ The following environment variables are supported:
 
    Default system locale.
 
+ * `HOSTNAME` (Default: "raspberrypi" )
+
+   Setting the hostname to the specified value.
+
  * `KEYBOARD_KEYMAP` (Default: "gb" )
 
    Default keyboard keymap.