add instruction how to build usql with oracle sql support

aur/usql/README.md

@@ -0,0 +1,31 @@
+install `pacman -S go extra/unixodbc core/pkgconf`  
+
+install from aur
+  * oracle-instantclient-basic
+  * oracle-instantclient-sdk
+
+
+use this `oci8.pc`
+
+```
+libdir=/usr/lib/client64/lib
+includedir=/usr/include
+
+glib_genmarshal=glib-genmarshal
+gobject_query=gobject-query
+glib_mkenums=glib-mkenums
+
+Name: oci8
+Description: oci8 library
+Libs: -L${libdir} -lclntsh
+Cflags: -I${includedir}
+Version: 18.3
+```
+
+then `export PKG_CONFIG_PATH=~/`
+
+do ` go get -u -tags all github.com/xo/usql`
+
+and add `~/go/bin` to `$PATH`
+
+done.