Add doxygen documentation to libosmocoding

This adds the minimum amount of API documentation that we should have on
all our code, particularly new code merged into a library.

Change-Id: I526804f64313867913574e50e5b9e9205ad3aa74
diff --git a/include/osmocom/coding/gsm0503_coding.h b/include/osmocom/coding/gsm0503_coding.h
index f6591f5..55375bb 100644
--- a/include/osmocom/coding/gsm0503_coding.h
+++ b/include/osmocom/coding/gsm0503_coding.h
@@ -3,6 +3,14 @@
 #include <stdint.h>
 #include <osmocom/core/bits.h>
 
+/*! \addtogroup coding
+ *  @{
+ */
+
+/*! \file gsm0503_coding.h
+ *  \brief GSM TS 05.03 coding
+ */
+
 #define GSM0503_GPRS_BURSTS_NBITS	(116 * 4)
 #define GSM0503_EGPRS_BURSTS_NBITS	(348 * 4)
 #define NUM_BYTES(N) ((N + 8 - 1) / 8)
@@ -61,3 +69,5 @@
 
 int gsm0503_sch_encode(ubit_t *burst, const uint8_t *sb_info);
 int gsm0503_sch_decode(uint8_t *sb_info, const sbit_t *burst);
+
+/*! @} */