doc: Update README.md with metadata retrieval instructions and testing caveats (#6156)

packages/types-support/src/metadata/README.md

@@ -49,7 +49,31 @@ To retrieve the runtime versions -
 
 - Add it to the relevant folders e.g. `v14/{kusama, polkadot, substrate}-ver.ts`
 
-NOTE: This all works for manual updating, but for an easier process run from root for each respective chain: `node ./scripts/metadata-get.mjs`
+## NOTE: 
+
+1. This all works for manual updating, but for an easier process run from root for each respective chain: `node ./scripts/metadata-get.mjs`.
+
+2. If the chain is already live, running it locally is unnecessary — update the metadata & types using `node ./scripts/metadata-get.mjs --url <ws_chain_url>`.
+
+3. Run `yarn test:one packages/types/src/metadata/v14` for Metadata checks
+
+## Caveat
+
+Occasionally, running the tests may result in a failure due to outdated metadata. The error message might look like this:
+
+```bash
+    /api/packages/types/src/metadata/v14/Metadata.spec.ts
+
+    undefined / undefined
+```
+
+### How to Fix
+
+1. Navigate to the file mentioned in the error.
+2. Paste the line `writeJson(json, version, type, 'json');` into the `try` block.
+3. Rerun the tests — they should pass now.
+4. **Important:** After verifying that the tests pass, revert your changes and run the tests again to ensure everything still works as expected.
+
 
 ## extraction (Legacy)
 
@@ -67,4 +91,4 @@ To retrieve the metadata -
 
 - Add it to the relevant folders e.g. `v14/{kusama, polkadot, substrate}-hex.json`
 - Run `yarn build:interfaces` to re-generate all TS
-- Run `yarn test:one packages/types/src/metadatra/v14` for Metadata checks
+- Run `yarn test:one packages/types/src/metadata/v14` for Metadata checks