add "unixtime" to the MFM cheatsheet

packages/frontend/src/components/SkMfmWindow.vue

@@ -99,6 +99,16 @@ SPDX-License-Identifier: AGPL-3.0-only
 						</div>
 					</div>
 				</div>
+				<div class="section _block">
+					<div class="title">{{ i18n.ts._mfm.unixtime }}</div>
+					<div class="content">
+						<p>{{ i18n.ts._mfm.unixtimeDescription }}</p>
+						<div class="preview">
+							<Mfm :text="preview_unixtime"/>
+							<MkTextarea v-model="preview_unixtime"><template #label>MFM</template></MkTextarea>
+						</div>
+					</div>
+				</div>
 				<div class="section _block">
 					<div class="title">{{ i18n.ts._mfm.inlineCode }}</div>
 					<div class="content">
@@ -429,6 +439,9 @@ const preview_small = ref(
 const preview_center = ref(
 	`<center>${i18n.ts._mfm.dummy}</center>`,
 );
+const preview_unixtime = ref(
+	`$[unixtime ${Math.floor(Date.now() / 1000)}]`,
+);
 const preview_inlineCode = ref('`<: "Hello, world!"`');
 const preview_blockCode = ref(
 	'```ai\n~ (#i, 100) {\n\t<: ? ((i % 15) = 0) "FizzBuzz"\n\t\t.? ((i % 3) = 0) "Fizz"\n\t\t.? ((i % 5) = 0) "Buzz"\n\t\t. i\n}\n```',