create explorer project folder and readme

explorer/README.md

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+# Sui Explorer
+A chain explorer for the Sui network, similiar in functionality to [Etherscan](https://etherscan.io/) or [Solana Explorer](https://explorer.solana.com/).
+
+## Proposed Basic Architecture
+
+This is described in order of how data flows, from the source network to the end usder.
+
+* We get raw data from the network using the in-progress "bulk sync" API
+
+    This raw data is dumped into a document store / noSQL kind of DB (which one not decided yet).
+
+    Plenty of the Cosmos explorers use this step, citing how much easier it makes syncing history & recovering from periods of being offline. Access to untouched historical data means that any errors in converting the data into relational table form can be corrected later.
+
+* A sync process runs to move new data from this raw cache into a more structured, relational database. 
+
+    This DB is PostgreSQL, unless there's a strong argument for using something else presented. 
+
+    We index this database to optimize common queries - "all transactions for an address", "objects owned by address", etc. 
+
+* The HTTP api is implemented as a Rust webserver, talks to the relational database & encodes query results as JSON
+
+* Browser frontend is a standard React app, powered by the HTTP api
+
+
+## Sub-Projects
+
+Front-end code goes in `client` folder,
+
+All back-end pieces (historical data store, relational DB, & HTTP layer) go in `server` sub-folders.

explorer/client/README.md

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+# Sui Explorer Client
+
+The front-end project goes here, along with a description of how to build it.

explorer/server/README.md

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+# Sui Explorer Server
+
+All pieces of the explorer that run on a server (history store, relational DB, HTTP layer) will have subprojects in here.