README.md: confusing mention of "rebase"

[peter-kehl]

README.md & Marketplace reads: edit the tour's ref by right-clicking it in the CodeTour tree and selecting Change Git Ref. This let's you "rebase" a tour to a tag/commit...

However:

1. Have a tour with GIT commit reference
2. Modify the source code above (before) a tour step (tour step having line)
3. Commit (the source code change) to GIT.
4. Change the tour's GIT reference to the new commit.

Mainstream understanding/use of term rebase implies that the above steps would update the tour step to have a line number from the new GIT commit. (I'd assume there could be an API to get the line shifts (per file) between two GIT commits for some changes, depending on how GIT generates the deltas.)

Please

• implement the above expected behavior (for line-based steps) - especially so if pattern-based steps are likely to be far away, and/or
• update README.md and Marketplace to reflect the reality (to save people's confusion and time).
• don't close this as a "duplicate" of Regex implementation for tour resiliency #141, because then people will stay in the dark.

Thank you in advance.