Add memo docs (solana-labs#160)

* Add memo docs

* nudge

docs/src/memo.md

@@ -2,5 +2,28 @@
 title: Memo Program
 ---
 
-A simple program that accepts a string of encoded characters and verifies that
-it parses. Currently handles UTF-8.
+A simple program that validates a string of UTF-8 encoded characters.  It can be
+used to record a string on-chain, stored in the instruction data of a successful
+transaction.
+
+## Background
+
+Solana's programming model and the definitions of the Solana terms used in this
+document are available at:
+- https://docs.solana.com/apps
+- https://docs.solana.com/terminology
+
+## Source
+
+The Memo Program's source is available on
+[github](https://github.com/solana-labs/solana-program-library)
+
+## Interface
+
+The on-chain Memo Program is written in Rust and available on crates.io as
+[spl-memo](https://crates.io/crates/spl-memo).
+
+## Operational overview
+
+The Memo program attempts to UTF-8 decode the instruction data; if successfully
+decoded, the instruction is successful.

docs/src/token.md

@@ -22,8 +22,7 @@ The Token Program's source is available on
 ## Interface
 
 The on-chain Token Program is written in Rust and available on crates.io as
-[spl-token](https://docs.rs/spl-token/1.0.2/spl_token/). The program's
-[instruction interface]
+[spl-token](https://docs.rs/spl-token). The program's [instruction interface
 documentation](https://docs.rs/spl-token/1.0.2/spl_token/instruction/enum.TokenInstruction.html)
 can also be found there.
 

memo/README.md

@@ -1,4 +1,7 @@
 # Memo Program
 
-A simple program that accepts a string of encoded characters and verifies that
-it parses. Currently handles UTF-8.
+A simple program that validates a string of UTF-8 encoded characters.  It can be
+used to record a string on-chain, stored in the instruction data of a successful
+transaction.
+
+Full documentation is available at https://spl.solana.com