Refer to glob(7) for metachar listing in spec.md

Rather than listing all the rules, just refer the reader to the man
page.  Although brace expansion isn't part of the standard rules, we
still support it through glob(3), so make a note.

docs/manual/spec.md

@@ -651,13 +651,11 @@ Supported modifiers are:
 
 ### Shell Globbing
 
-The usual rules for shell globbing apply.  Metacharacters can be escaped by
-prefixing them with a backslash (`\`).  A backslash or percent sign can be
-escaped with an extra `\` or `%`, respectively.  Spaces are used to separate
-file names and must be escaped by enclosing the file name in quotes.
-
-The metacharacters supported are wildcards (`*` and `?`), square brackets
-(`[]`), and curly braces (`{}`).
+The usual rules for shell globbing apply (see `glob(7)`), including brace
+expansion.  Metacharacters can be escaped by prefixing them with a backslash
+(`\`).  A backslash or percent sign can be escaped with an extra `\` or `%`,
+respectively.  Spaces are used to separate file names and must be escaped by
+enclosing the file name in quotes.
 
 For example: