Add Avro reference, add links (#252)

* Add Avro reference, add links

Based on [#251 issue) I made.
I also added links to the relevant packages.

* Update README.md

Co-authored-by: Jacob Quinn <quinn.jacobd@gmail.com>

README.md

@@ -58,8 +58,8 @@ It currently doesn't include support for:
   * C data interface
 
 Third-party data formats:
-  * csv and parquet support via the existing CSV.jl and Parquet.jl packages
-  * Other Tables.jl-compatible packages automatically supported (DataFrames.jl, JSONTables.jl, JuliaDB.jl, SQLite.jl, MySQL.jl, JDBC.jl, ODBC.jl, XLSX.jl, etc.)
-  * No current Julia packages support ORC or Avro data formats
+  * CSV, parquet and avro support via the existing [CSV.jl](https://github.com/JuliaData/CSV.jl), [Parquet.jl](https://github.com/JuliaIO/Parquet.jl) and [Avro.jl](https://github.com/JuliaData/Avro.jl) packages
+  * Other Tables.jl-compatible packages automatically supported ([DataFrames.jl](https://github.com/JuliaData/DataFrames.jl), [JSONTables.jl](https://github.com/JuliaData/JSONTables.jl), [JuliaDB.jl](https://github.com/JuliaData/JuliaDB.jl), [SQLite.jl](https://github.com/JuliaDatabases/SQLite.jl), [MySQL.jl](https://github.com/JuliaDatabases/MySQL.jl), [JDBC.jl](https://github.com/JuliaDatabases/JDBC.jl), [ODBC.jl](https://github.com/JuliaDatabases/ODBC.jl), [XLSX.jl](https://github.com/felipenoris/XLSX.jl), etc.)
+  * No current Julia packages support ORC
 
 See the [full documentation](https://arrow.juliadata.org/dev/) for details on reading and writing arrow data.