doc: indicate createSecureContext arg is optional

The `options` argument to `tls.createSecureContext()` is optional.

Indicate this by using `[` and `]` in the function signature.

PR-URL: #22545
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: George Adams <george.adams@uk.ibm.com>

doc/api/tls.md

@@ -1003,7 +1003,7 @@ as arguments instead of options.
 A port or host option, if specified, will take precedence over any port or host
 argument.
 
-## tls.createSecureContext(options)
+## tls.createSecureContext([options])
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 added: v0.11.13
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