feat(remaining_dist_eta): update readme

Signed-off-by: Ahmed Ebrahim <ahmed.ebrahim@leodrive.ai>

Author: Ahmed Ebrahim

planning/autoware_remaining_distance_time_calculator/README.md

@@ -15,22 +15,24 @@ This package aims to provide mission remaining distance and remaining time calcu
 | ------------- | ------ | ------------- | --------------------------- |
 | `update_rate` | double | 10.0          | Timer callback period. [Hz] |
 
-### Inner-workings / Algorithms
+### Inner-workings
 
-### Remaining Distance Calculation
+#### Remaining Distance Calculation
 
 - The remaining distance calculation is based on getting the remaining shortest path between the current vehicle pose and goal pose using `lanelet2` routing APIs.
 - The remaining distance is calculated by summing the 2D length of remaining shortest path, with exception to current lanelet and goal lanelet
   - For the current lanelet, the distance is calculated from the current vehicle position to the end of that lanelet
   - For the goal lanelet, the distance is calculated from the start of the lanelet to the goal pose in this lanelet.
+- When there is only one lanelet remaining, the distance is calculated by getting the 2D distance between the current vehicle pose and goal pose.
+- Checks are added to handle cases when current lanelent, goal lanelet, or routing graph are not valid to prevent node process die
+  - In such cases when, last valid remaining distance and time are maintained
 
-### Remaining Time Calculation
+#### Remaining Time Calculation
 
-- Remaining time is calculated using simple equation of motion by getting the current vehicle velocity magnitude.
-- Then the calculated remaining distance is divided by the velocity magnitude.
+- The remaining time currently depends on a simple equation of motion by getting the maximum velocity limit.
+- The remaining distance is calculated by dividing remaining distance by the maximum velocity limit
 
 ### Future Work
 
 - Find a more efficient way for remaining distance calculation instead of regularly searching the graph for finding the remaining shortest path
-- Engage more sophisticated motion models for more accurate remaining time calculations
-- Handle cases when the vehicle stops during the mission or Autoware get disengaged then engaged for the same mission
+- Engage more sophisticated motion models for more accurate remaining time calculations