dev.md: updated documentation

doc/dev.md

@@ -179,6 +179,26 @@ configuration could be detected as blank while it's not. Only one parameter will
 be accepted, a bloc device. The bloc device you provide is suposed to be a whole
 drive, not a partition.
 
+#### 4.2.3. ```mkparts  <disk> [dos|gpt] [size_part1 [... size_partN]]```
+This function create partitions on the disk given as the first parameter. The 
+second parameter can be gpt or dos, respectively to instruct the creation of a
+GPT partition table (which is default when not mentioned) or a DOS partition
+table, deprecated but suported for compatibility purposes. Then a list of size
+can be given to generate more than one partition. In the case of a DOS partition
+table, only primary partition are possible, four of it maximum.
+
+Partition size can be :
+ - simple number: will be interpreted as a precise number of cylinder, this is
+ the only method that will be precise;
+ - 100M: will create a 100 MiB partition, more or less to the nearest cylinder;
+ - 100G: will create a 100 GiB partition, more or less to the nearest cylinder;
+ - 100T: same again 100 TiB, ang you really have a lot of space...
+ - 0: will be interpreted as all remaining space in the final partition scheme.
+ It must come only once.
+
+Be warned that a size (whatever the unit is) can result in slightly different
+space depending on the drive model and cylinder size.
+
 ### 4.3. Other functionnalities
 That file don't profide any other things that the previously listed functions.