CIP-0010 | Add label-in-use query, clean up update process (#1171)

* remove unclear language + add Koios query from @katomm

* add long time recommentations for CIP-0010 PRs

* apply some long-missing transitional punctuation

* change `tag` to `label`, more explicit instructions on process

Author: rphair

CIP-0010/README.md

@@ -46,17 +46,20 @@ transaction_metadata =
 
 ### Structure
 
-These are the reserved `transaction_metadatum_label` values
+These are the reserved `transaction_metadatum_label` values:
 
 `transaction_metadatum_label` | description
 ----------------------------  | -----------------------
-0 - 15                        | reserved\*
+0 - 15                        | reserved
 65536 - 131071                | reserved - private use
 
-For the registry itself, please see [registry.json](./registry.json) in the machine-readable format. Please open your pull request against
-this file.
+For the registry itself, please see [registry.json](./registry.json). To add or modify a label definition, please open a pull request against this file. For new label numbers, include background information about your project and/or documentation of the label if available (and state your intended usage if not).
 
-\* It's best to avoid using `0` or any a similar number like `1` that other people are very likely to use. Prefer instead to generate a random number
+You can check if a label number is already in use with an API query.  For instance: to check if label `8414` is in use via Koios (no API key needed for `curl`):
+
+```
+curl -s "https://api.koios.rest/api/v1/tx_by_metalabel?_label=8414" -H "accept: application/json"
+```
 
 ## Rationale: how does this CIP achieve its goals?