Improve documentations accessibility of links and text contrast

[sudo-may]

• pages links are indicated via color greem; grayscale, color-blind and low vision users will not be able to differentiate those links
• using axe and wave to uncover contrast issues

[sudo-may]

pr: https://github.com/NationalSecurityAgency/skills-docs/pull/224

[sudo-may]

nice resource: https://github.com/vue-a11y/vuepress-theme-default-vue-a11y