Update how-can-i-help.md

[roshniRam]

Update Coding, Documentation and Quality Assurance, design and important Sugar Labs links.

[quozl]

Thanks. Reviewed.

• the first change is not approved; the existing wording is correct,
• the second change is not approved; the existing wording is adequate,
• the third change is approved; it was a typo,
• the commit message doesn’t say what the problem was and why it is being fixed.

[quozl]

2ee03a277b30eae79a65eb21beff39f5b6c5c65b