Add release notes script to PUBLISHING.md

[styfle]

This script can be used every time we publish.

It obviously wont create a GitHub release but it can be used to generate the text to copy/pasta into a GitHub release.

This will work for canary or master, as long as we run it each time before lerna publishes.

It is the responsibility of the person publishing to select the proper tag, probably always use now@* for stable releases.

[codecov-io]

Codecov Report

Merging #3006 into canary will increase coverage by 1.3%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           canary    #3006     +/-   ##
=========================================
+ Coverage   11.98%   13.28%   +1.3%     
=========================================
  Files         268      268             
  Lines       10189    10336    +147     
  Branches     1297     1223     -74     
=========================================
+ Hits         1221     1373    +152     
- Misses       8875     8901     +26     
+ Partials       93       62     -31

Impacted Files	Coverage Δ
src/util/prefer-v2-deployment.ts	56.25% <0%> (-5.66%)	⬇️
src/util/projects/get-project-by-id-or-name.ts	25% <0%> (-3.58%)	⬇️
src/util/metrics.ts	70.58% <0%> (+2.4%)	⬆️
src/util/dev/builder-cache.ts	80.74% <0%> (+3.47%)	⬆️
src/util/dev/router.ts	82.69% <0%> (+4.12%)	⬆️
src/util/dev/builder.ts	77.41% <0%> (+4.34%)	⬆️
src/util/dev/yarn-installer.ts	90.74% <0%> (+5.02%)	⬆️
src/util/dev/server.ts	66.43% <0%> (+5.73%)	⬆️

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[TooTallNate]

Why not just run release (with no arguments) after doing the lerna publishing?

[styfle]

@TooTallNate Because release doesn't work with tags that are not semver. Also it doesn't respect the idea of monorepos which have multiple packages using different versions (I know because I tried it this morning).