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tsdb documenation: Improve Chunk documentation

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Signed-off-by: Antoine Pultier <45740+fungiboletus@users.noreply.github.com>

Signed-off-by: Antoine Pultier <45740+fungiboletus@users.noreply.github.com>
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10
tsdb/docs/format/chunks.md
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@ -29,16 +29,16 @@ in-file offset (lower 4 bytes) and segment sequence number (upper 4 bytes).
# Chunk
```
┌───────────────┬───────────────────┬──────────────┬─────────────────┐
│ len <uvarint> │ encoding <1 byte> │ data <bytes> │ CRC32C <4 byte> │
└───────────────┴───────────────────┴──────────────┴─────────────────┘
┌───────────────┬───────────────────┬──────────────┬───────────────────┐
│ len <uvarint> │ encoding <1 byte> │ data <bytes> │ checksum <4 byte> │
└───────────────┴───────────────────┴──────────────┴───────────────────┘
```
Notes:
* `<uvarint>` has 1 to 10 bytes, from [`encoding/binary`](https://go.dev/src/encoding/binary/varint.go).
* `len`: Chunk size in bytes. Encoded using 1 to 10 bytes, using the [`<uvarint>` encoding](https://go.dev/src/encoding/binary/varint.go).
* `encoding`: Currently either `XOR` (1), `histogram` (2), or `float histogram` (3).
* `data`: See below for each encoding.
* `CRC32C`: CRC32 Castagnoli of `encoding` and `data`, serialised as an unsigned 32 bits big endian.
* `checksum`: Checksum of `encoding` and `data`. It's a [cyclic redudancy check](https://en.wikipedia.org/wiki/Cyclic_redundancy_check) with the Castagnoli polynomial, serialised as an unsigned 32 bits big endian number. Can be refered as a `CRC-32C`.
## XOR chunk data