Added explanation on how to it manually

README.md

@@ -2,6 +2,21 @@
 
 This script will convert the dsv save from drastic emulator to a melonDS save file
 
+### Usage
+
+```bash
+usage: dr2mds.py [-h] [-o OUTPUT] [-f] file
+
+positional arguments:
+  file                  The drastic save file
+
+optional arguments:
+  -h, --help            show this help message and exit
+  -o OUTPUT, --output OUTPUT
+                        Specify the output file
+  -f, --force           Overwrite the output file if it exists
+```
+
 ### How to use
 
 You need python 3 installed.  
@@ -18,7 +33,7 @@ You can also specify the output like
 ./dr2mds.py "Pokemon Black.dsv" -o "PKMN.sav"
 ```
 
-### How this works ?
+### How does this works ?
 
 MelonDS determines the type of save using exact byte count in the save file
 
@@ -37,3 +52,21 @@ dd if=Pokemon.dsv of=Pokemon.sav bs=1 count=524288
 ```
 
 This will make a 4KiB EEPROM save from drastic to melonDS save.
+
+### How to calculate the save size
+
+Run `wc -c file` in terminal to count the number of bytes in the file
+
+```bash
+wc -c Pokemon\ Black.dsv
+```
+
+which will output something like
+
+```
+524410 Pokemon Black.dsv
+```
+
+Now calculate log(524410)/log(2) which equates to 19.000335671081253  
+Take its floor i.e. 19 and calculate the power of 2 to the number ie 2<sup>19</sup> which equates to 524288
+The resulting number is the number of blocks to put in `dd count=` if you are manually making the save.