Add doc comment to ParseWithClaims (golang-jwt#232)

parser.go

@@ -42,6 +42,10 @@ func (p *Parser) Parse(tokenString string, keyFunc Keyfunc) (*Token, error) {
 	return p.ParseWithClaims(tokenString, MapClaims{}, keyFunc)
 }
 
+// ParseWithClaims parses, validates, and verifies like Parse, but supplies a default
+// object implementing the Claims interface. This provides default values which
+// can be overridden and allows a caller to use their own type, rather than
+// the default MapClaims implementation of Claims.
 func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyfunc) (*Token, error) {
 	token, parts, err := p.ParseUnverified(tokenString, claims)
 	if err != nil {