[css-pseudo-4] Latest Bikeshed is choking on punctuation in code blocks.

* Escapes brackets to avoid fatal error
* Adds issue about Bikeshed eating pipes

See speced/bikeshed#2202

Author: fantasai

css-pseudo-4/Overview.bs

@@ -342,8 +342,10 @@ First-Letter Text: ''::first-letter'' pseudo-element and its ''::prefix'' and ''
     (P (Zs|P)*)? (L|N|S)+ ((Zs|P−(Ps|Pd))* (P−(Ps|Pd))?</code>
     or, alternatively,
     <code highlight="bnf" style="font-family: inherit">
-    ([P] [Zs P]*)? [L N S]+ ([[Zs] [P--[Ps Pd]]]* [P--[Ps Pd]])?</code>
+    (&#91;P] [Zs P]*)? [L N S]+ ([Zs [P--[Ps Pd]]]* [P--[Ps Pd]])?</code>
     <!-- this is not actually BNF, but it highlights better that way -->
+
+    ISSUE: Bikeshed is <a href="https://github.com/tabatkins/bikeshed/issues/2202">eating punctuation</a> in this note, which is not helpful.
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