Improve example code.

Author: emadda

readme.md

@@ -20,48 +20,65 @@ You also need to install an IO provider.
 See `./test/all` for detailed usage.
 
 
+#### Get a file ref
 ```javascript
-
 // Note: Example is for Node.js.
 const {smpi} = require("sqlite-mpi-client-js");
 const iop = require("smpi-iop-node-ffi");
 
 const c = smpi.newClient(iop);
 const f = c.newFileRef("/tmp/db-file.sqlite");
+```
+
+#### Write transactions
+
+- There is only one active write transaction at a time per SQLite file.
+    - This applies at an OS level, for all processes.
+
+- Write tx requests will queue when there is an active outstanding write tx.
+    - Queued write tx requests will resolve in First In First Out (FIFO) manner.
+    - When the promise returned from `f.getWriteTx()` resolves, the `wtx` is active.
 
 
-// Write Transaction.
+```javascript
 const wtx = await f.getWriteTx();
 
 // `q` can be a read or write with write txs.
 await wtx.q("SELECT 1+1");
+
 await wtx.read("SELECT 1+1");
+
 await wtx.write("INSERT ...");
 
 await wtx.commit();
 // await wtx.rollback();
+```
 
+#### Read transactions
 
+- Read transactions are concurrent; you can have many read transactions active and reading from the same database file.
 
-// Read Transaction.
+```javascript
 const rtx = await f.getReadTx();
 
 // `q` must be a read.
-const rtx = await f.getReadTx();
 await rtx.q("SELECT 1+1");
 
 await rtx.read("SELECT 1+1");
 
 // No writes.
 // await tx.write("INSERT ...");
 
-
 await rtx.commit();
 // await rtx.rollback();
+```
+
 
 
+#### Params
 
-// Params
+
+```javascript
 const wtx = await f.getWriteTx();
 
 // Index based.
@@ -71,7 +88,7 @@ await wtx.write("INSERT INTO t1 (b) VALUES (?1), (?2)", [3, 4]);
 // Key based.
 await wtx.write("INSERT INTO t1 (b) VALUES (:x), (:y)", {x: 1, y: 2});
 await wtx.write("INSERT INTO t1 (b) VALUES (@x), (@y)", {x: 1, y: 2});
-await rtx.commit();
+await wtx.commit();
 ```
 
 ### Notes