What is gaia intro to docs (#3294)

docs/.vuepress/config.js

@@ -37,6 +37,7 @@ module.exports = {
         title: "Gaia",
         collapsable: false,
         children: [
+          "/gaia/what-is-gaia"
           "/gaia/installation",
           "/gaia/join-testnet",
           "/gaia/validators/validator-setup",

docs/gaia/what-is-gaia.md

@@ -0,0 +1,22 @@
+# What is Gaia?
+
+`gaia` is the name of the Cosmos SDK application for the Cosmos Hub. It comes with 2 main entrypoints:
+
+- `gaiad`: The Gaia Daemon, runs a full-node of the `gaia` application.
+- `gaiacli`: The Gaia command-line interface, which enables interraction with a Gaia full-node.
+
+`gaia` is built on the Cosmos SDK using the following modules:
+
+- `x/auth`: Accounts and signatures.
+- `x/bank`: Token transfers.
+- `x/staking`: Staking logic.
+- `x/mint`: Inflation logic.
+- `x/distribution`: Fee distribution logic.
+- `x/slashing`: Slashing logic.
+- `x/gov`: Governance logic.
+- `x/ibc`: Inter-blockchain transfers.
+- `x/params`: Handles app-level parameters.
+
+>About the Cosmos Hub: The Cosmos Hub is the first Hub to be launched in the Cosmos Network. The role of a Hub is to facilitate transfers between blockchains. If a blockchain connects to a Hub via IBC, it automatically gains access to all the other blockchains that are connected to it. The Cosmos Hub is a public Proof-of-Stake chain. Its staking token is called the Atom.
+
+Next, learn how to [install Gaia](./installation.md).