Resolve "Documentation to import new Trackers"

Related to #45

ingress/README.md

@@ -50,8 +50,26 @@ For each domain to be imported, an entry should be created in the ./config/tikiw
 * The certificate to access the SmartData API should be stored in the config directory and described in the configuration.
 * The tracker properties defines the name of the trackers (as stored in the TikiWiki) to retrieve the data.
 * The api property defines the base url for the API (such as https://iot.lisha.ufsc.br)
+* The Trackers element contains a mapping where the mapped value (right) is the name of the Tracker in TikiWiki from which to extract the data.
+
+### Basic information
+The import process from the TikiWiki currently assumes that a domain contains three Trackers: 
+Vehicles, VehicleMaintenancePlan, VehicleMaintenanceReport and VehicleMaintenanceReportErrorCodes. 
+The first three trackers are specific for each domain. The last one can be shared between different 
+domains since it a list of standard error codes.
+
+### Extending/modifying the current import process
+
+To modify/extend the current process the class app/command/tikiwiki/ImportCommand.php must be changed. 
+The process method is responsible for calling the required functions and execute the import process for each domain. 
+Thus, to add a new Tracker or edit the process of current ones, the necessary methods in this class should be modified.
+
+The class contains several helpers methods to facilitate the conversion process - such as unit conversions and 
+dynamic TikiWiki Tracker field mappings. The existing methods serve as good guideline on how to implement/extend the 
+existing code.
 
 # Pipeline development
 
 * Create a new Command (./app/command) following the syntax of existing commands (such as tikiwiki/ImportCommand.php)
-* Register the new Command at ./setup.php
\ No newline at end of file
+* Register the new Command at ./setup.php
+