Add options and explanations to README

Author: dmeehan1968

as-lib/README.md

@@ -2,4 +2,14 @@
 
 **WIP**
 
-This directory is provided to allow LoRaMac-node to be built as a static library for inclusion in other projects.
+This directory is provided to allow LoRaMac-node to be built as a static library for inclusion in other projects.
+
+## CMake Options
+
+- LORAMAC_AS_LIB:BOOL Whether to build the project as a static library (when ON), or to build the example applications
+- LORAMAC_SUFFIX:STRING Defaults to empty, but can be set to any string to allow for multiple static libraries to
+  be build (for example with different region support)
+- LORAMAC_SECURE_ELEMENT Name of the secure element, defaults to SOFT_SE
+- LORAMAC_SECURE_ELEMENT_PRE_PROVISIONED Whether the secure element is pre-provisioned (default ON)
+- LORAMAC_SOFT_SE_AES_DEC_PREKEYED Whether the SOFT SE secure elements AES support is DEC Prekeyed (default ON)
+- LORAMAC_RADIO Name of the radio driver, defaults to SX1276