message: [docs] change privacy.md reference to main repo
  While looking at the documentation on data collection, I noticed that
  the link to `privacy.md` was broken. This commit points the link to the
  main repo.
diff: @@ -44,4 +44,5 @@ You can opt-out of telemetry by re-running the bootstrap-vcpkg script with -disa
  passing --disable-metrics to vcpkg on the command line,
  or by setting the VCPKG_DISABLE_METRICS environment variable.
  -Read more about vcpkg telemetry at docs/about/privacy.md
  +Read more about vcpkg telemetry at [docs/about/privacy.md](https://github.com/microsoft/vcpkg/blob/master/docs/about/privacy.md)
  +in the main repository
  