Remove backticks from ranges describing valid identifiers (#1321)

This is really to fix the inconsistency that was there.

Author: foolip

docs/README.md

@@ -50,7 +50,7 @@ Feature authors should (in descending order of priority):
 
 ### Identifiers
 
-Feature identifiers must contain only lowercase alphanumeric characters (`a`-`z` and `0-9`) plus the `-` character (hyphen or minus sign) as a word separator.
+Feature identifiers must contain only lowercase alphanumeric characters (a-z and 0-9) plus the `-` character (hyphen or minus sign) as a word separator.
 
 The identifier should match the name, with these additional guidelines: