docs: various fixes (#28208)

Co-authored-by: Evgeni Chasnovski <evgeni.chasnovski@gmail.com>
Co-authored-by: Famiu Haque <famiuhaque@proton.me>
Co-authored-by: Gregory Anders <greg@gpanders.com>
Co-authored-by: Guilherme Soares <guilhermesoares1970@gmail.com>
Co-authored-by: Jannik Buhr <jannik.m.buhr@gmail.com>
Co-authored-by: thomaswuhoileong <72001875+thomaswuhoileong@users.noreply.github.com>
Co-authored-by: tom-anders <13141438+tom-anders@users.noreply.github.com>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>

src/nvim/eval.lua

@@ -7902,6 +7902,7 @@ M.funcs = {
     name = 'printf',
     params = { { 'fmt', 'any' }, { 'expr1', 'any' } },
     signature = 'printf({fmt}, {expr1} ...)',
+    returns = 'string',
   },
   prompt_getprompt = {
     args = 1,

src/nvim/eval/userfunc.c

@@ -2365,7 +2365,7 @@ void ex_function(exarg_T *eap)
   // Read the body of the function, until ":endfunction" is found.
   if (KeyTyped) {
     // Check if the function already exists, don't let the user type the
-    // whole function before telling him it doesn't work!  For a script we
+    // whole function before telling them it doesn't work!  For a script we
     // need to skip the body to be able to find what follows.
     if (!eap->skip && !eap->forceit) {
       if (fudi.fd_dict != NULL && fudi.fd_newkey == NULL) {

src/nvim/options.lua

@@ -1324,7 +1324,7 @@ return {
       defaults = { if_true = '' },
       desc = [=[
         A template for a comment.  The "%s" in the value is replaced with the
-        comment text.  For example, C uses "/*%s*/". Currently only used to
+        comment text. For example, C uses "/*%s*/". Used for |commenting| and to
         add markers for folding, see |fold-marker|.
       ]=],
       full_name = 'commentstring',

src/nvim/vvars.lua

@@ -64,9 +64,10 @@ M.vars = {
   },
   completed_item = {
     desc = [=[
-      Dictionary containing the most recent |complete-items| after
-      |CompleteDone|.  Empty if the completion failed, or after
-      leaving and re-entering insert mode.
+      Dictionary containing the |complete-items| for the most
+      recently completed word after |CompleteDone|.  Empty if the
+      completion failed, or after leaving and re-entering insert
+      mode.
       Note: Plugins can modify the value to emulate the builtin
       |CompleteDone| event behavior.
     ]=],