Mention community-maintained themes #1017

Job	Run time
lint	18s
ruby-versions / Generate Ruby versions	2s
test (3.0, ubuntu-latest)	25s
test (3.0, macos-latest)	23s
test (3.0, windows-latest)	1m 43s
test (3.1, ubuntu-latest)	29s
test (3.1, macos-latest)	24s
test (3.1, windows-latest)	1m 16s
test (3.2, ubuntu-latest)	23s
test (3.2, macos-latest)	23s
test (3.2, windows-latest)	1m 56s
test (3.3, ubuntu-latest)	24s
test (3.3, macos-latest)	20s
test (3.3, windows-latest)	2m 41s
test (head, ubuntu-latest)	32s
test (head, macos-latest)	26s
test (head, windows-latest)	1m 13s
test (jruby, ubuntu-latest)	2m 7s
test (jruby, macos-latest)	1m 43s
test (jruby-head, ubuntu-latest)	1m 59s
test (jruby-head, macos-latest)	1m 15s
test (truffleruby, ubuntu-latest)	2m 19s
test (truffleruby, macos-latest)	2m 24s
test (truffleruby-head, ubuntu-latest)	3m 12s
test (truffleruby-head, macos-latest)	4m 44s
	33m 1s

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