[Config, Docs] Add gateway staking config documentation (#321)

* docs: Add gateway staking config documentation

* Edits to docusaurus/docs/configs/gateway_staking_config.md

---------

Co-authored-by: Daniel Olshansky <[email protected]>

docusaurus/docs/configs/gateway_staking_config.md

@@ -0,0 +1,56 @@
+---
+title: Gateway staking config
+sidebar_position: 5
+---
+
+# Gateway staking config <!-- omit in toc -->
+
+This document describes the configuration file used by the `Gateway` actor
+to submit a stake transaction required to allow it to serve Pocket Network
+RPC services.
+
+- [Usage](#usage)
+- [Configuration](#configuration)
+  - [`stake_amount`](#stake_amount)
+- [Example](#example)
+
+## Usage
+
+The `stake-gateway` transaction submission command accepts a `--config` flag
+that points to a `yaml` configuration file that defines the `stake_amount` the
+`Gateway` is willing to lock.
+
+:::warning
+
+TestNet is not ready as of writing this documentation so you may
+need to adjust the command below appropriately.
+
+:::
+
+```bash
+poktrolld tx gateway stake-gateway \
+  --home=./poktroll \
+  --config ./stake_config.yaml \
+  --keyring-backend test \
+  --from gateway1 \
+  --node tcp://poktroll-node:36657
+```
+
+## Configuration
+
+The configuration file consists of the `stake_amount` entry denominated in `upokt`.
+
+### `stake_amount`
+
+_`Required`_
+
+```yaml
+stake_amount: <number>upokt
+```
+
+Defines the amount of `upokt` to stake by the `Gateway` to be able to serve
+`RelayRequest` on the Pocket network on behalf of `Application`s.
+
+## Example
+
+A full example of the configuration file could be found at [gateway_staking_config.yaml](https://github.com/pokt-network/poktroll/tree/main/localnet/poktrolld/config/gateway1_stake_config.yaml)