Update markdown documents

While working on the task YT-73 Documentation: Update the style for the generated html file, we found several problems in the existing documents.

And this MR is intended to fix the discovered issues:

• docs:readme: remove "guf" leftovers
• docs:readme: update links:
  • update poky, openembedded, meta-qt5 links to https. So they can be viewed in browser and still be cloned via git.
  • fix wrong link to meta-freescale-distro.
  • update link to Ubuntu ISO image.
• docs:whats-new: fix broken links:
  • NXP linux kernel migrated to GitHub from codeaurora.
  • Weston migrated to freedesktop.org GitLab from GitHub.
• docs:whats-new: fix id for chapters
• removed whitespaces in all markdown documents