Update 03-02-parser.rst to mention BNF notation for Vala Grammar

Help people find Vala BNF grammar easier from search engines.

Author: colinkiama

source/contributor-guide/compiler-guide/03-00-the-vala-compiler/03-02-parser.rst

@@ -279,8 +279,8 @@ Error Handling
 I don't want to spoil your fun too much by going into the details of the parser, other than that every parse\_ function can throw a ParseError. ParseError is caught when parsing a block or the declarations of a namespace, class, struct, or interface. Fixme.
 
 
-Grammar of Vala
----------------
+Grammar of Vala (BNF Notation)
+------------------------------
 
 This grammar is hand-generated from Vala.Parser. Sometimes the structure of this grammar diverges slightly from the code, for example optional non-terminal symbols. However the non-terminal symbol names usually match a parse\_ method in Vala.Parser.
 
@@ -609,4 +609,4 @@ More literal-specific grammar at https://gnome.pages.gitlab.gnome.org/vala/manua
    local_variable ::= identifier [ inline_array_type ] [ "=" expression ]
    
    expression_statement ::= statement_expression ";"
-   
+