clean the page, introduce quick guide

Author: ericrgz

src/protocol/pay-per-task.md

@@ -1,20 +1,20 @@
----
-title: Pay Per Task Model
-description:
-  Pricing model and task categories for iExec protocol, including computing and
-  deal time limits.
----
 
-# Pay per task model
+# Task size (Pay-Per-Task)
 
-We are introducing a new method for pricing and we have defined several task
-categories that describe the execution boundaries. We'll setup a test
-infrastructure so that application developers can evaluate the category of their
-submissions. Conversely, worker pools will be able to benchmark their
-infrastructures against the reference machine.
+Pay-per-task categories, time limits, and claim rules.
 
-In the future, we'll redefine the categories, and provide more advanced tools
-for helping developers to maximize the usage of the infrastructure
+
+## Pay-per-task model
+
+The pay-per-task model is based on task size categories. Each category defines
+two limits:
+
+- Maximum Computing Time (C): per-task execution time on the worker. If the task
+  exceeds C, the task is stopped and failed.
+- Maximum Deal Time (D): overall time window for a task in the deal. If the task
+  isn’t completed within D, the requester can claim (i.e., recover according to
+  protocol rules). On claim, the requester recovers the RLC escrowed for that
+  task, no payout is made to the worker and workerpool.
 
 **Categories Description:**
 
@@ -23,12 +23,23 @@ for helping developers to maximize the usage of the infrastructure
 | 0 – XS       | 5 min                          | 50 min                    |
 | 1 – S        | 20 min                         | 200 min (3h20m)           |
 | 2 – M        | 1 hour                         | 10h                       |
-| 3 – L        | 3 hour                         | 30h (1d6h)                |
-| 4 – XL       | 10 hour                        | 100h (4d4h)               |
-
-- Each worker will allocate **C** minutes to compute the application. If the
-  computation is not completed within this **Maximum Computing Time**, the
-  running application will be stopped.
-- From a buyer perspective, a requester will be able to claim a task of a deal
-  after **D** minutes if the task is not completed within the **Maximum Deal
-  Time**.
+| 3 – L        | 3 hours                        | 30h (1d6h)                |
+| 4 – XL       | 10 hours                       | 100h (4d4h)               |
+
+- Workers allocate up to C per task. Beyond C, the app is stopped.
+- Requesters can claim after D if the task isn’t completed.
+
+## How to pick a category (quick guide)
+
+Use this decision table to choose a safe category for your workload.
+
+| **Typical workload**                  | **Suggested category** |
+| ------------------------------------- | ---------------------- |
+| Short scripts / small data processing | Cat 0–1                |
+| Medium data processing (10-15min)     | Cat 2                  |
+| Heavy ML inference / long simulations | Cat 3–4                |
+
+Use the iExec SDK (CLI/API) to **set the category** in app, request, or
+workerpool orders.  
+For commands and examples, see the
+[iExec SDK GitHub repository](https://github.com/iExecBlockchainComputing/iexec-sdk/blob/master/docs/README.md).