Document that we support srfi-62 and add it to %cond-expand-features.

* module/ice-9/boot-9.scm (%cond-expand-features): Add srfi-62.

* doc/ref/srfi-modules.texi (SRFI-0): Add srfi-62 to the list of core
  features.
  (SRFI-62): New node.

module/ice-9/boot-9.scm

@@ -4043,6 +4043,7 @@ when none is available, reading FILE-NAME with READER."
     srfi-39  ;; parameterize
     srfi-55  ;; require-extension
     srfi-61  ;; general cond clause
+    srfi-62  ;; s-expression comments
     srfi-105 ;; curly infix expressions
     ))