[Documentation]: Standardise restructured text

Nobody has claimed this yet.

### Contact Details

_No response_

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

Use a linter (e.g., `doc8`, `rstcheck`, etc) to check integrity of restructured text. Ignoring the line lengths issues, there are ~40 errors reported by `doc8`.

```
./documentation/source/index.rst:103: D002 Trailing whitespace
./documentation/source/index.rst:117: D002 Trailing whitespace
./documentation/source/index.rst:122: D002 Trailing whitespace
./documentation/source/index.rst:130: D002 Trailing whitespace
./documentation/source/index.rst:131: D002 Trailing whitespace
./documentation/source/index.rst:132: D002 Trailing whitespace
./documentation/source/index.rst:136: D002 Trailing whitespace
./documentation/source/index.rst:144: D002 Trailing whitespace
./documentation/source/index.rst:145: D002 Trailing whitespace
./documentation/source/index.rst:150: D002 Trailing whitespace
./documentation/source/index.rst:158: D002 Trailing whitespace
./documentation/source/index.rst:159: D002 Trailing whitespace
./documentation/source/getting_started/index.rst:19: D002 Trailing whitespace
./documentation/source/getting_started/index.rst:20: D002 Trailing whitespace
./documentation/source/how_it_works/parallelism/lfric_mpi.rst:18: D002 Trailing whitespace
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:45: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:46: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:54: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:58: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:59: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:60: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:62: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:63: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:123: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:124: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:125: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:222: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:223: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:224: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:261: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:262: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:297: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_configuration_namelists.rst:298: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_generators.rst:62: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_generators.rst:64: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_generators.rst:65: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_generators.rst:66: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_generators.rst:68: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/meshes/mesh_generators.rst:69: D003 Tabulation used for indentation
./documentation/source/how_to_use_it/parallelism/lfric_message_passing_interface.rst:26: D002 Trailing whitespace
./documentation/source/how_to_contribute/coding_standards/fortran_coding_standards.rst:315: D000 Bullet list ends without a blank line; unexpected unindent.
./documentation/source/how_to_contribute/coding_standards/fortran_coding_standards.rst:353: D002 Trailing whitespace
./documentation/source/how_to_contribute/coding_standards/fortran_coding_standards.rst:355: D002 Trailing whitespace
```

### Further details of the issue.

_No response_

Start by running doc8 against the files under documentation/source listed in the issue, while ignoring line-length findings. Fix the reported trailing whitespace, tab indentation, and bullet-list formatting without changing the documentation content. Done means the listed D002, D003, and D000 errors no longer appear.

Written by the indexing model from the issue text.