Update documentation

README.md

 # CCSDSpy
 
+---
+
 CCSDSpy is a library to read a data packet coming from a space mission that follows the Consultative Committee for Space Data Systems (CCSDS) standard
 
 Current version **0.1.0**
 
-Installation
-Usage
+[[_TOC_]]
+
+## Installation
+## Usage
 ```python
 from CCSDS import CCSDS
 
@@ -13,11 +17,59 @@ dat = CCSDS('BepiColombo',packet)
 ```
 wehre *packet* is a string with the HEX rappresentation of the pachet
 
-Limitation
+## Limitation
 
 ## Data Structure
 
-The CCSDS Header is composed by two blocks 
+The CCSDS Header is composed by two blocks:
++ the Source Packet Header 
++ the Packet Data Field
+
+The first one il long 48 bits the second one has a varble dimension and structure depending by the type and the content of the packet. in [Figure 1](#figure-1-telemetry-packet) is reported the structure for a Telemetry Packet.
 
+The structure of the CCSDS class follow the structure of the packet header.
+
+
+```mermaid
+classDiagram
+    CCSDS --|> SPH
+    CCSDS --|> PDF
+    SPH --|> packetID
+    SPH--|> sequenceControl
+    PDF --|> DFHeader
+    class CCSDS{
+        + str Data 
+    }
+    class DFHeader{
+        + uint PUSVersion
+        + uint ServiceType
+        + uint ServiceSubType
+        + uint DestinationId
+        + uint Synchronization
+        + uint CorseTime
+        + uint FineTime
+        + str SCET
+        + str  UTCTime
+    }
+    class SPH{
+        + uint packetLength
+    }
+    class packetID{
+        + uint VersionNum
+        + uint packetType
+        + uint dataFieldHeaderFlag 
+        + uint Apid
+        + uint Pid
+        + uint Pcat
+    }
+    class sequenceControl{
+        + bin SegmentationFlag
+        + uint SSC
+    }
+    class PDF{
+        +str Data
+    }
+```
 
-![TM packet](docs/TM_Packet_H_eader.png)
+![TM packet](docs/TM_Packet_Header.png "Telemetry packet")
+####Figure 1 - Telemetry Packet

ccsds.py

@@ -2,6 +2,7 @@
 from bitstring import BitStream
 import spiceypy as spice
 
+# Versio 0.1.0
 
 class PacketId:
     def __init__(self,data):