Update font renderer example to avoid number to string ambiguity

If someone would add numeric characters (say `0`) like in the affected example, this error would occur:
```
      Must be string, got <class 'esphome.helpers.EInt'>. did you forget putting quotes around the value?.
      - 0
```
Instead, the numeric characters should be listed in a string with the other plain ones. The specials can still be added on new rows, even with commas if desired.

Author: nagyrobi

components/font.rst

@@ -52,12 +52,13 @@ Next, create a ``font:`` section in your configuration:
         size: 28
         bpp: 4
         glyphs: [
-          a,A,á,Á,e,E,é,É,
+          0123456789aAáÁeEéÉ,
           (,),+,-,_,.,°,•,µ,
-          "\u0020", #space
-          "\u0021", #!
-          "\u0022", #"
-          "\u0027", #'
+          "\u0020", # space
+          "\u002C", # ,
+          "\u0021", # !
+          "\u0022", # "
+          "\u0027", # '
           ]
 
       - file: "fonts/RobotoCondensed-Regular.ttf"