add list of standardized tags.

Author: fiatjaf

README.md

@@ -77,6 +77,20 @@ Please update these lists when proposing NIPs introducing new event kinds.
 
 When experimenting with kinds, keep in mind the classification introduced by [NIP-16](16.md).
 
+## Standardized Tags
+
+| name       | value                   | other parameters  | NIP                      |
+| ---------- | ----------------------- | ----------------- | ------------------------ |
+| e          | event id (hex)          | relay URL, marker | [1](01.md), [10](10.md)  |
+| p          | pubkey (hex)            | relay URL         | [1](01.md)               |
+| r          | a reference (URL, etc)  |                   | [12](12.md)              |
+| t          | hashtag                 |                   | [12](12.md)              |
+| g          | geohash                 |                   | [12](12.md)              |
+| nonce      | random                  |                   | [13](13.md)              |
+| subject    | subject                 |                   | [14](14.md)              |
+| d          | identifier              |                   | [33](33.md)              |
+| expiration | unix timestamp (string) |                   | [40](40.md)              |
+
 ## Criteria for acceptance of NIPs
 
 1. They should be implemented in at least two clients and one relay -- when applicable.