docs: fix typo Update README.md (#12702)

<img width="508" alt="Снимок экрана 2025-01-08 в 22 14 05"
src="https://github.com/user-attachments/assets/9a8b630b-463a-4973-a4e6-17b2be0010ad"
/>

"become validator": Should be "become a validator" (missing the article
"a").

Corrected.

README.md

@@ -70,7 +70,7 @@ You can join all the active networks:
 
 Check the `nearup` repository for [more details](https://github.com/near/nearup) on how to run with or without docker.
 
-To learn how to become validator, checkout [documentation](https://docs.near.org/docs/develop/node/validator/staking-and-delegation).
+To learn how to become a validator, checkout [documentation](https://docs.near.org/docs/develop/node/validator/staking-and-delegation).
 
 ## Contributing