docs(clue): improve example for <Leader> key submode

Related to #2185

Author: echasnovski

doc/mini-clue.txt

@@ -369,7 +369,8 @@ In this module submode can be implemented following these steps:
   this submode, pressing its prefix will be automatically emulated (leading
   back to being inside submode).
 
-- Register submode prefix (or some of its starting part) as trigger.
+- Register submode prefix (or some of its starting part) as trigger. Do not
+  register "overlapping" triggers, like `<Leader>` and `<Leader>m`.
 
 ## Submode examples ~
 
@@ -395,10 +396,14 @@ In this module submode can be implemented following these steps:
 
   require('mini.clue').setup({
     triggers = {
-      { mode = 'n', keys = '<Leader>m' },
-      { mode = 'x', keys = '<Leader>m' },
+      -- This can also set up directly `<Leader>m` as a trigger, but make
+      -- sure to not also use `<Leader>`, as they would "overlap"
+      { mode = 'n', keys = '<Leader>' },
+      { mode = 'x', keys = '<Leader>' },
     },
     clues = {
+      { mode = 'n', keys = '<Leader>m', desc = '+Move' },
+
       { mode = 'n', keys = '<Leader>mh', postkeys = '<Leader>m' },
       { mode = 'n', keys = '<Leader>mj', postkeys = '<Leader>m' },
       { mode = 'n', keys = '<Leader>mk', postkeys = '<Leader>m' },

lua/mini/clue.lua

@@ -365,7 +365,8 @@
 ---   this submode, pressing its prefix will be automatically emulated (leading
 ---   back to being inside submode).
 ---
---- - Register submode prefix (or some of its starting part) as trigger.
+--- - Register submode prefix (or some of its starting part) as trigger. Do not
+---   register "overlapping" triggers, like `<Leader>` and `<Leader>m`.
 ---
 --- ## Submode examples ~
 ---
@@ -391,10 +392,14 @@
 ---
 ---   require('mini.clue').setup({
 ---     triggers = {
----       { mode = 'n', keys = '<Leader>m' },
----       { mode = 'x', keys = '<Leader>m' },
+---       -- This can also set up directly `<Leader>m` as a trigger, but make
+---       -- sure to not also use `<Leader>`, as they would "overlap"
+---       { mode = 'n', keys = '<Leader>' },
+---       { mode = 'x', keys = '<Leader>' },
 ---     },
 ---     clues = {
+---       { mode = 'n', keys = '<Leader>m', desc = '+Move' },
+---
 ---       { mode = 'n', keys = '<Leader>mh', postkeys = '<Leader>m' },
 ---       { mode = 'n', keys = '<Leader>mj', postkeys = '<Leader>m' },
 ---       { mode = 'n', keys = '<Leader>mk', postkeys = '<Leader>m' },