Uplift the contributions guide to include a reference to checking readme text and comments

[andyblundell]

Adding, to the contributions guide, a reference to the "Consider comments and Readme text" principle (in the "Create knowledge" chapter)

(Also removed a couple of references to NHSD)

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud