add: table of contents to docs

README.md

@@ -4,6 +4,16 @@ The `helpers` package contains Solana helper functions, for use in the browser a
 
 Eventually most of these will end up in `@solana/web3.js`.
 
+## What can I do with this module?
+
+[Resolve a custom error message](#getcustomerrormessageprogramerrors-errormessage)
+[Get an airdrop, and wait until it's confirmed](#requestandconfirmairdropconnection-publickey-lamports)
+[Get an airdrop if your balance is below some amount](#requestandconfirmairdropifrequiredconnection-publickey-lamports-maximumbalance)
+[Get a Solana Explorer link for a transaction, address, or block](#getexplorerlinktype-identifier-clustername)
+[Get a keypair from a keypair file (like id.json)](#getkeypairfromfilefilename)
+[Get a keypair from an environment variable](#getkeypairfromenvironmentenvironmentvariable)
+[Add a new keypair to an env file](#addkeypairtoenvfilekeypair-environmentvariable-file)
+
 ## Installation
 
 ```bash