Improvement of Doxycomments in the CCSDS FDP checksum class

[JackNWhite]

Related Issue(s)	n
Has Unit Tests (y/n)	n
Documentation Included (y/n)	y

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Change Description

• General improvement of the class Doxycomments, in particular those of the class itself and of the update() method.
• Fixed/reinstated a broken link in the contributions readme.

Rationale

Usage of the class, particularly the update() method, was ambiguous and the existing comments were unclear.

[LeStarch]

I added a comment about consistency for block comments.

[thomas-bc]

I just recently watched a talk about the power and importance of documentation so thank you very much for this!

[LeStarch]

CI failure is being investigated.

[LeStarch]

Ignoring known CI failure.