Writev syscall comments and tests

[rupeshkoushik07]

Description

This PR adds description and tests to writev syscall.
Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Test A - lind_project/tests/test_cases/test_a.c
• Test B - lind_project/tests/test_cases/test_b.c

Checklist:

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been added to a pull request and/or merged in other modules (native-client, lind-glibc, lind-project)