Added description for make config

Author: danielinux

docs/compile.md

@@ -7,6 +7,23 @@ To enable specific compile options, use environment variables while calling make
 
 `make CORTEX_M0=1`
 
+As an alternative, you can provide a .config file in the root directory of wolfBoot.
+Command line options have priority on `.config` options, as long as .config options are
+defined using the `?=` operator, e.g.:
+
+`WOLFBOOT_PARTITION_BOOT_ADDRESS?=0x14000`
+
+## Generate a new configuration
+
+A new `.config` file with a set of default parameters
+can be generated by running `make config`. The build script will ask to enter a default value for
+each configuration parameter. Enter confirm the current value, indicated in between `[]`.
+
+Once a .config file is in place, it will change the default compile-time options when running `make`
+without parameters.
+
+.config can be modified with a text editor to alter the default options later on.
+
 ## Platform selection
 
 If supported natively, the target platform can be specified using the `TARGET` variable.
@@ -27,9 +44,9 @@ By default, wolfBoot is compiled for ARM Cortex-M3/4/7. To compile for Cortex-M0
 
 ### Flash partitions
 
-The file [include/target.h](../include/target.h) must be modified according to flash geometry,
+The file [include/target.h](../include/target.h) is generated according to the configured flash geometry,
 partitions size and offset of the target system. The following values must be set to provide the
-desired flash configuration:
+desired flash configuration, either via the command line, or using the .config file as 
 
 `WOLFBOOT_SECTOR_SIZE`