Add some documentation on asynchronous queries

README.md

@@ -19,6 +19,7 @@ LibPQ.jl is a Julia wrapper for the PostgreSQL `libpq` C library.
   * UTF-8 client encoding
 * Queries
   * Create and execute queries with or without parameters
+  * Execute queries asynchronously
   * Stream results using [Tables](https://github.com/JuliaData/Tables.jl)
   * Configurably convert a variety of PostgreSQL types to corresponding Julia types (see the **Type Conversions** section of the docs)
 * Prepared Statements

docs/src/index.md

@@ -20,6 +20,12 @@ data = columntable(result)
 result = execute(conn, "SELECT typname FROM pg_type WHERE oid = \$1", ["16"])
 data = columntable(result)
 
+# the same but asynchronously
+async_result = async_execute(conn, "SELECT typname FROM pg_type WHERE oid = \$1", ["16"])
+# do other things
+result = fetch(async_result)
+data = columntable(result)
+
 close(conn)
 ```
 

src/asyncresults.jl

@@ -165,6 +165,9 @@ Calling `fetch` on the `AsyncResult` will return a [`Result`](@ref).
 All keyword arguments are the same as [`execute`](@ref) and are passed to the created
 `Result`.
 
+Only one `AsyncResult` can be active on a [`Connection`](@ref) at once.
+If multiple `AsyncResult`s use the same `Connection`, they will execute serially.
+
 `async_execute` does not yet support [`Statement`](@ref)s.
 
 `async_execute` optionally takes a `parameters` vector which passes query parameters as