docs: Add validator SOL reqs

docs/src/running-validator/validator-reqs.md

@@ -2,6 +2,13 @@
 title: Validator Requirements
 ---
 
+## Minimum SOL requirements
+
+There is no strict minimum amount of SOL required to run a validator on Solana.
+However a vote account is required, which has a rent-exempt reserve of
+0.02685864 SOL. Voting also requires sending a vote tranasaction for each block
+the validator agrees with, which can cost up to 1.1 SOL per day.
+
 ## Hardware Recommendations
 
 - CPU