Added Advanced chapter.

Author: DariuszDepta

docs/core/advanced/_category_.json

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+{
+  "label": "Advanced",
+  "position": 6,
+  "link": {
+    "type": "doc",
+    "id": "advanced"
+  }
+}

docs/core/advanced/advanced.md

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+---
+title: Advanced
+---
+
+# Advanced topics
+
+In this part of the documentation, we go over some more "advanced" things you can do with the
+functionality CosmWasm core offers.
+
+:::tip
+
+While the name of this section is "advanced", this doesn't mean that we want to imply that you
+only need these functions in advanced contexts. The wording "advanced" more so refers to the fact
+that you should be familiar with endpoints, the structs that are passed to the endpoints, etc.
+
+:::

docs/core/advanced/measuring-time.md

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+---
+sidebar_position: 1
+---
+
+# Measuring time
+
+Accessing the current time is useful in a lot of different contexts but time is hard.
+It is hard to coordinate, hard to keep in sync, and this gets worse in distributed settings such as blockchains.
+
+In CosmWasm, we solve this by passing you some information about the blockchain you are running on
+whenever an entrypoint is invoked.
+
+In each of the entrypoints, you get a parameter of the type `Env` and this struct contains the field `block`.
+The struct contained in this field has a bunch of different information about the current state of the blockchain
+you are running on.
+
+:::tip
+
+The documentation for the `BlockInfo` struct can be [found here].
+
+:::
+
+The timestamp contained in this struct can be safely used in your program as the source of the current time.
+Well, kinda. It won't be 100% matching the current time, as it is the timestamp of the block we are currently
+operating on.
+
+But you can rely on this timestamp to have the following properties:
+
+- Consistent across the chain (every validator on the chain has the same info)
+- Monotonic (it will only ever increase or stay the same; never decrease)
+
+Read more about [BFT Time] and [Proposer-Based Timestamps (PBTS)][PBTS] if you want to better understand
+where the time value comes from.
+
+[found here]: https://docs.rs/cosmwasm-std/latest/cosmwasm_std/struct.BlockInfo.html
+[BFT Time]: https://docs.cometbft.com/main/spec/consensus/bft-time
+[PBTS]: https://informal.systems/blog/introducing-proposer-based-timestamps-pbts-in-cometbft