README: mention bootloader

Author: Ivan-Velickovic

README.md

@@ -7,8 +7,9 @@
 
 The purpose of the seL4 Microkit is to enable system designers to create static software systems based on the seL4 microkernel.
 
-The seL4 Microkit consists of three parts:
+The seL4 Microkit consists of four parts:
 
+   * Microkit bootloader
    * Microkit library
    * Microkit initial task
    * Microkit tool