Improve English language in TechOverview.md

[johnnonweiler]

I have gone through TechOverview.md, fixed some spelling mistakes, and made some suggestions for slightly rewording a few sentences.

Checklist

• [x] Source is rebased on latest upstream main so is mergeable automatically or easily merged even with confliction.
• [x] Title of this PR is meaningful: e.g. "fix issue #8 geomPipeline.py -o does not work", not "fix geomPipeline.py"
• [x] Commit message is meaningful: git push origin +your_branch to squash some tiny fixes for CI failures
• [x] Give the maintainer the legal rights to change the open source license in the future (see wiki/Contribution.md) for details

[qingfengxia]

thank you john