Update 'README.md'

README.md

@@ -19,6 +19,10 @@ ___
 - [Managing OpenPGP Keys](https://riseup.net/en/security/message-security/openpgp/gpg-keys) *(added 5/3/2023)*
 - [Defense Intelligence Headquarters - 情報本部](https://en.wikipedia.org/wiki/Defense_Intelligence_Headquarters) *(added 5/4/2023)*
 - [XKeyscore](https://en.wikipedia.org/wiki/XKeyscore) *(added 5/4/2023)*
+- [Key server](https://en.wikipedia.org/wiki/Key_server_(cryptographic)) *(added 5/5/2023)*
+- [End-to-end encryption](https://en.wikipedia.org/wiki/End-to-end_encryption) *(added 5/5/2023)*
+- [Telegram Video Calls](https://telegram.org/blog/video-calls) *(added 5/5/2023)*
+- [End-to-end Encrypted Voice and Video Calls](https://core.telegram.org/api/end-to-end/video-calls) *(added 5/5/2023)*
 
 ## [Mathematics and Computer Science](mathematics.md)
 - [OEIS: The Online Encyclopedia of Integer Sequences](https://oeis.org/)