update readme with constant flag

Author: unreal

README.md

@@ -42,31 +42,32 @@ Run `fexcel help` for more information on usage.
 
 ## Global Flags
 
-|   | Flag       | Type   | Description | Default |
-| - | ---------- | ----   | ----------- | ------- |
-|   | --ains     | string | start cell\* of analog input ids | |
-|   | --aouts    | string | start cell\* of analog output ids | |
-|   | --dins     | string | start cell\* of digital input ids | |
-|   | --douts    | string | start cell\* of digital output ids | |
-|   | --flags    | string | start cell\* of flag ids | |
-|   | --gins     | string | start cell\* of group input ids | |
-|   | --gouts    | string | start cell\* of group output ids | |
-| -h| --help     |        | help for fexcel | |
-|   | --noupdate |        | don't check for fexcel updates | |
-|   | --numregs  | string | start cell\* of numeric register ids | |
-|   | --offset   | int    | column offset between ids and comments | 1 |
-|   | --posregs  | string | start cell\* of position register ids | |
-|   | --rins     | string | start cell\* of robot input ids | |
-|   | --routs    | string | start cell\* of robot output ids | |
-|   | --save     |        | save flagset to config file | |
-|   | --sheet    | string | default sheet to look at when unspecified in the start cell\* | "Sheet1" |
-|   | --sregs    | string | start cell\* of string register ids | |
-|   | --timeout  | int    | timeout value in seconds (default 5) |
-|   | --ualms    | string | start cell\* of user alarm ids | |
+|   | Flag        | Type   | Description | Default |
+| - | ----------- | ----   | ----------- | ------- |
+|   | --ains      | string | start cell\* of analog input ids | |
+|   | --aouts     | string | start cell\* of analog output ids | |
+|   | --constants | string | start cell\* of constant definitions | |
+|   | --dins      | string | start cell\* of digital input ids | |
+|   | --douts     | string | start cell\* of digital output ids | |
+|   | --flags     | string | start cell\* of flag ids | |
+|   | --gins      | string | start cell\* of group input ids | |
+|   | --gouts     | string | start cell\* of group output ids | |
+| -h| --help      |        | help for fexcel | |
+|   | --noupdate  |        | don't check for fexcel updates | |
+|   | --numregs   | string | start cell\* of numeric register ids | |
+|   | --offset    | int    | column offset between ids and comments | 1 |
+|   | --posregs   | string | start cell\* of position register ids | |
+|   | --rins      | string | start cell\* of robot input ids | |
+|   | --routs     | string | start cell\* of robot output ids | |
+|   | --save      |        | save flagset to config file | |
+|   | --sheet     | string | default sheet to look at when unspecified in the start cell\* | "Sheet1" |
+|   | --sregs     | string | start cell\* of string register ids | |
+|   | --timeout   | int    | timeout value in seconds (default 5) |
+|   | --ualms     | string | start cell\* of user alarm ids | |
 
 \**start cell flags can be optionally prefixed with a sheet name that
 overrides the default `-sheet` flag. (e.g. `--numregs Data:A2`). They
-can also include a custom offset (e.g. `--dins IO:A2:6) where digital
+can also include a custom offset (e.g. `--dins 6:IO:A2) where digital
 inputs are located on the "IO" sheet starting at A2 and the comments
 are in column G.*