Added IAEA API

with correct formatting

README.md

@@ -1395,6 +1395,7 @@ API | Description | Auth | HTTPS | CORS |
 | [arXiv](https://arxiv.org/help/api/user-manual) | Curated research-sharing platform: physics, mathematics, quantitative finance, and economics | No | Yes | Unknown |
 | [CORE](https://core.ac.uk/services#api) | Access the world's Open Access research papers | `apiKey` | Yes | Unknown |
 | [GBIF](https://www.gbif.org/developer/summary) | Global Biodiversity Information Facility | No | Yes | Yes |
+| [IAEA](https://www-nds.iaea.org/relnsd/vcharthtml/api_v0_guide.html) | Physical properties of all elements and isotopes | No | Yes | Yes |
 | [iDigBio](https://github.com/idigbio/idigbio-search-api/wiki) | Access millions of museum specimens from organizations around the world | No | Yes | Unknown |
 | [inspirehep.net](https://github.com/inspirehep/rest-api-doc) | High Energy Physics info. system | No | Yes | Unknown |
 | [isEven (humor)](https://isevenapi.xyz/) | Check if a number is even | No | Yes | Unknown |