guide: add docs for sending funds (#24)

add send docs

pages/web/send.mdx

@@ -1 +1,8 @@
-# Sending Funds
+# Sending Funds
+
+You can use the Send page to send and receive tokens inside Penumbra's multi-asset shielded pool. You can select what asset you want to send by clicking the asset name on the send page. Fees can be paid in the native staking token by default, or alternate fee tokens such as OSMO or USDC. Like other blockchains, the fee tier determines priority for inclusion in the next block. 
+
+Penumbra transactions also include a `memo` field, but unlike other blockchains, this memo field can only be read by the receiver of the transaction.
+
+To receive funds, navigate to the 'Receive' tab on the send page. Here you can select what account to use to receive funds, but it's safe and privacy-preserving to receive multiple times to the same address. Unless you have a specific reason to, there's no need to check the "IBC Deposit Address" switch; for most use cases, you should simply use the "Shield Funds" tab to perform IBC deposits.
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