Recent changes

Clarified "shared noteheads"

Use Mac OS - specific makefile for "make revision" step, otherwise there's an error "grep: /proc/cpuinfo: No such file or directory".

I changed the name of tip "Test a PR submitted by someone else" into "Test someone else's branch" because that is actually what those instructions do. I think the instructions I added "Fetch all PRs submitted to upstream" are more useful for getting *PR's that have actually been submitted to musescore upstream". My instructions are easier because you don't have to remember a long command...you just have to type "git checkout upstream/pr/####" after fetching upstream. No need to remember and type someone's github username and their branch name, just the PR #. Also I made some readability tweaks.

actually seemed a little big for the Advice & Tips, so I lowered to

changed to syntax highlighting

added tip about fetching all PRs from upstream musescore.

Lots of corrections to buttons

Seems to me this belongs alongside figured bass, cross-staff beaming and shared noteheads.

Link to Noteheads page

Added fuller explanation to "Note properties"

https://musescore.org/en/node/99176 to be verified?

Changed title to reflect page topic

Expanded some text for clarity.

Added some anchor tabs.