docs(api-and-naming): elaborate on the argument list

Co-authored-by: Ville Skyttä <[email protected]>

Author: akinomyoga

doc/api-and-naming.md

@@ -144,7 +144,7 @@ concept is later extended to also mean "eXported".
 The generator functions, which have names of the form `_comp_compgen_NAME`, are
 used to generate completion candidates.  A generator function is supposed to be
 called by `_comp_compgen [OPTS] NAME ARGS` where `OPTS = -aR|-v var|-c cur|-C
-dir|-U var|-P pref` are the options to modify the behavior (see the code
+dir|-U var|-P prefix` are the options to modify the behavior (see the code
 comment of `_comp_compgen` for details).  When there are no `opts`, the
 generator function is supposed to be directly called as `_comp_compgen_NAME
 ARGS`.  The result is stored in the target variable (which is `COMPREPLY` by