update contribution guidelines

Signed-off-by: Guillaume W. Bres <[email protected]>

CONTRIBUTING.md

@@ -21,10 +21,18 @@ depending on which type of RINEX we're talking about.
 For complex RINEX formats like Navigation Data, that module will contain all possible inner types.
 
 Other important structures :
+- `src/epoch/mod.rs`: the Epoch module basically provides
+hifitime::Epoch parsing methods, because RINEX describes date in non standard formats.
+Also, the `Flag` structure is used to mark Observations (valid or invalid).
 - `src/constellation.rs` defines GNSS constellations
 - `src/constellation/augmentation.rs` : preliminary SBAS support
 - `src/sv.rs` defines a Satellite vehicle, which is associated to a constellation
-  - src/hatanaka/mod.rs : the Hatanaka module contains the RINEX Compressor and Decompressor 
+- `src/observable.rs`: defines possible observations like raw phase
+- `src/carrier.rs`: defines carrier signals in terms of frequency and bandwidth.
+It also contains utilities to identify which GNSS signals we're dealing with,
+from an `Observable`.
+- `src/hatanaka/mod.rs`: the Hatanaka module contains the RINEX Compressor and Decompressor 
+- `src/antex/antenna.rs`: defines the index structure of ANTEX format
 
 NAV RINEX
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