Doxygen link appears to be broken.

[maggiehendry]

The Doxygen link in the working practices appears to be broken.

https://github.com/MetOffice/simulation-systems/blame/f02f2f0f5322e66a93e08d2c49cf26c331c3d892/source/WorkingPractices/documentation.rst#L18

[yaswant]

@james-bruten-mo that should read: https://code.metoffice.gov.uk/trac/lfric/wiki/LFRicTechnical/Documentation/DoxygenUsage