Create mermaid diagram for Coretime (#268)

* adds mermaid diagram to describe coretime

* Apply suggestions from code review

Co-authored-by: Nicolás Hussein <80422357+nhussein11@users.noreply.github.com>

---------

Co-authored-by: Nicolás Hussein <80422357+nhussein11@users.noreply.github.com>

polkadot-protocol/architecture/polkadot-chain/agile-coretime.md

@@ -9,6 +9,15 @@ description: Explore the efficient scheduling mechanisms to access Polkadot core
 
 Agile Coretime is the [scheduling](https://en.wikipedia.org/wiki/Scheduling_(computing)){target=\_blank} framework on Polkadot that lets parachains efficiently access cores, which comprise an active validator set tasked with parablock validation. As the first blockchain to enable a flexible scheduling system for blockspace production, Polkadot offers unparalleled adaptability for parachains.
 
+``` mermaid
+graph TB
+    A[Cores Designation]
+    B[Bulk Coretime]
+    C[On-Demand Coretime]
+    A --continuous--> B
+    A --flexible--> C 
+```
+
 Cores can be designated to a parachain either continuously through [bulk coretime](#bulk-coretime) or dynamically via [on-demand coretime](#on-demand-coretime). Additionally, Polkadot supports scheduling multiple cores in parallel through [elastic scaling](https://wiki.polkadot.network/docs/learn-elastic-scaling){target=\_blank}, which is a feature under active development on Polkadot. This flexibility empowers parachains to optimize their resource usage and block production according to their unique needs.
 
 In this guide, you'll learn how bulk coretime enables continuous core access with features like interlacing and splitting, and how on-demand coretime provides flexible, pay-per-use scheduling for parachains. For a deep dive on Agile Coretime and its terminology, refer to the [Wiki doc](https://wiki.polkadot.network/docs/learn-agile-coretime#introduction-to-agile-coretime){target=\_blank}.