docs: Mention that msatoshi on pay is not optional, but ignored

Reported-by: Tim Horie <@thorie7912>
Signed-off-by: Christian Decker <@cdecker>

contrib/pylightning/lightning/lightning.py

@@ -285,8 +285,8 @@ class LightningRpc(UnixDomainSocketRpc):
 
     def pay(self, bolt11, msatoshi=None, description=None, riskfactor=None):
         """
-        Send payment specified by {bolt11} with optional {msatoshi}
+        Send payment specified by {bolt11} with {msatoshi}
-        (if and only if {bolt11} does not have amount),
+        (ignored if {bolt11} has an amount),
 
         {description} (required if {bolt11} uses description hash)
         and {riskfactor} (default 1.0)

lightningd/payalgo.c

@@ -695,8 +695,8 @@ static void json_pay(struct command *cmd,
 static const struct json_command pay_command = {
 	"pay",
 	json_pay,
-	"Send payment specified by {bolt11} with optional {msatoshi} "
+	"Send payment specified by {bolt11} with {msatoshi} "
-	"(if and only if {bolt11} does not have amount), "
+	"(ignored if {bolt11} has an amount), "
 	"{description} (required if {bolt11} uses description hash), "
 	"{riskfactor} (default 1.0), "
 	"{maxfeepercent} (default 0.5) the maximum acceptable fee as a percentage (e.g. 0.5 => 0.5%), "