spec out slashdash comments

Fixes: https://github.com/kdl-org/kdl/issues/22

README.md

@@ -95,6 +95,22 @@ bignum 1_000_000
 my-hex 0xdeadbeef
 my-octal 0o755
 my-binary 0b1010_1101
+
+// You can comment out individual nodes with /-. In the case below, everything
+// up until the closing `}` becomes commented.
+/-mynode "foo" key=1 {
+  a
+  b
+  c
+}
+
+// You can apply /- ("slashdash") comments to individual values, properties,
+// or child blocks, too:
+mynode /-"commented" "not commented" /-key="value" /-{
+  a
+  b
+}
+
 ```
 
 The following SDLang features are removed altogether:

SPEC.md

@@ -45,8 +45,9 @@ linespace := newline | ws | single-line-comment
 
 newline := ('\r' '\n') | '\n'
 
-ws := bom | ' ' | '\t' | multi-line-comment
+ws := bom | ' ' | '\t' | multi-line-comment | slashdash-comment
 
 single-line-comment := '//' ('\r' [^\n] | [^\r\n])* newline
 multi-line-comment := '/*' ('*' [^\/] | [^*])* '*/'
+slashdash-comment := '/-' (node | value | prop | node-children)
 ```