Change example of non-letter in version ordering

The "Package Formulas" grammar in the manual says that valid characters
for version numbers are `<identchar> | "+" | "." | "~"`. Notably this
does not include the "#" character. This change updates the example of a
comparing a letter to a non-letter character to use a non-letter
character that may appear in a version number.

Signed-off-by: Stephen Sherratt <[email protected]>

doc/pages/Manual.md

@@ -350,7 +350,7 @@ Here is a full example:
 >   1, which is the empty string `""`, is smaller than `"a"`.
 >
 > - For non-digit components, the ordering used is that letters are
->   always smaller than non-letters (for example `z` < `"#"`), while
+>   always smaller than non-letters (for example `z` < `"+"`), while
 >   non-letters are compared by ASCII order.
 >
 > - The `~` character is special as it sorts even before the end of sequence