Adding docs for updating metadata with grunt update, see phetsims/j…

…oist#497

checklists/updating_metadata.md

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+Updating metadata
+=============
+
+For anything that could potentially change checked-in top-level sim HTML or config files, the following should be done:
+
+- [ ] `perennial/bin/for-each.sh active-repos grunt update` (or run `grunt update` in affected repos)
+- [ ] Revert (partial) changes from interaction-dashboard's config that removes the custom line (see https://github.com/phetsims/interaction-dashboard/issues/83). This will be fixed at some point to not be needed.
+- [ ] If possible, run local aqua testing (`/aqua/test-server/test-sims.html?ea&audioVolume=0&testDuration=10000&testConcurrentBuilds=4&brand=phet&fuzzMouse`) to make sure nothing broke horribly.
+- [ ] git add the relevant files, commit (referencing the issue for the change) and push.
+
+This should be done for any changes to:
+
+- Preloads (build.json)
+- Dependencies (build.json or sim-specific phetLibs in package.json)
+- Package.json changes that affect what files should be generated (unit tests/colors/a11y/etc.)
+
+Note that for package.json changes that add flags, an automated process on bayes should update the perennial/data files automatically.