docs: make explicit that you can use ipfs cid format to convert both ways (#2126)

* Make explicit that you can use ipfs cid format to convert both ways

It took me a moment to realise that this was possible, so wanted to save that moment for future generations of IPFS newbies.

* docs: clarify dag-pb requirement for CIDv1 to CIDv0 conversion

add explicit note that conversion from CIDv1 to CIDv0 only works
when the CIDv1 uses dag-pb codec, as CIDv0 only supports dag-pb

---------

Co-authored-by: Andrew Gillis <[email protected]>
Co-authored-by: Marcin Rataj <[email protected]>

Author: 3 people

docs/concepts/content-addressing.md

@@ -145,7 +145,18 @@ v0.toV1().toString()
 //> 'bafybeihdwdcefgh4dqkjv67uzcmw7ojee6xedzdetojuzjevtenxquvyku'
 ```
 
-### v1 to v0 
+### v1 to v0
+
+Conversion from CIDv1 to CIDv0 is only possible when the CIDv1 uses the `dag-pb` codec (0x70), as CIDv0 only supports `dag-pb`. CIDs using other codecs like `raw` (0x55), `dag-cbor` (0x71), or `dag-json` (0x0129) cannot be converted to CIDv0.
+
+The built-in `ipfs cid format` command can be used to convert `dag-pb` from CIDv1 to CIDv0 from the command line:
+
+```
+$ ipfs cid format -v 0 bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi
+QmbWqxBEKC3P8tqsKc98xmWNzrzDtRLMiMPL8wBuTGsMnR
+```
+
+Note: The above example works because `bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi` uses the `dag-pb` codec. Attempting to convert a CIDv1 with a different codec will result in an error.
 
 Given a CID v1, JS users can convert back to v0 using the `toV0()` method provided by the [`multiformats`](https://www.npmjs.com/package/multiformats) library: