Update escrow readme

contracts/cw20-escrow/README.md

@@ -1,15 +1,29 @@
-# CW20 Basic
+# CW20 Escrow
 
-This is a basic implementation of a cw20 contract. It implements
-the [CW20 spec](../../packages/cw20/README.md) and is designed to
-be deloyed as is, or imported into other contracts to easily build
-cw20-compatible tokens with custom logic.
+This is an escrow meta-contract that allows multiple users to
+create independent escrows. Each escrow has a sender, recipient,
+and arbiter. It also has a unique id (for future calls to reference it)
+and an optional timeout.
 
-Implements:
+The basic function is the sender creates an escrow with funds.
+The arbiter may at any time decide to release the funds to either
+the intended recipient or the original sender (but no one else),
+and if it passes with optional timeout, anyone can refund the locked
+tokens to the original sender.
 
-- [x] CW20 Base
-- [ ] Mintable extension
-- [ ] Allowances extension
+We also add a function called "top_up", which allows anyone to add more
+funds to the contract at any time.
+
+## Token types
+
+This contract is meant not just to be functional, but also to work as a simple
+example of an CW20 "Receiver". And demonstrate how the same calls can be fed
+native tokens (via typical `HandleMsg` route), or cw20 tokens (via `Receiver` interface).
+
+Both `create` and `top_up` can be called directly (with a payload of native tokens),
+or from a cw20 contract using the [Receiver Interface](../../packages/cw20/README.md#receiver).
+This means we can load the escrow with any number of native or cw20 tokens (or a mix),
+allow of which get released when the arbiter decides.
 
 ## Running this contract
 
@@ -23,9 +37,9 @@ Once you are happy with the content, you can compile it to wasm via:
 
 ```
 RUSTFLAGS='-C link-arg=-s' cargo wasm
-cp ../../target/wasm32-unknown-unknown/release/cw20_base.wasm .
-ls -l cw20_base.wasm
-sha256sum cw20_base.wasm
+cp ../../target/wasm32-unknown-unknown/release/cw20_escrow.wasm .
+ls -l cw20_escrow.wasm
+sha256sum cw20_escrow.wasm
 ```
 
 Or for a production-ready (compressed) build, run the following from the
@@ -36,13 +50,5 @@ docker run --rm -v "$(pwd)":/code \
   --mount type=volume,source="cosmwasm_plus_cache",target=/code/target \
   --mount type=volume,source=registry_cache,target=/usr/local/cargo/registry \
   cosmwasm/rust-optimizer:0.8.0 ./contracts/cw20-base
-mv contract.wasm cw20_base.wasm
+mv contract.wasm cw20_escrow.wasm
 ```
-
-## Importing this contract
-
-You can also import much of the logic of this contract to build another
-ERC20-contract, such as a bonding curve, overiding or extending what you
-need.
-
-**TODO**