Include Kakadu notes in README.

image_server/README.md

@@ -1,6 +1,28 @@
 # Run iipsrv in a Docker container
 
-Build the container:
+In order to build this image server, a licensed version of Kakadu needs to be
+included in the source code. That has been excluded from this repository due
+to licensing constraints.
+
+Obtain the latest Kakadu SDK package and uncompress it in a new `kakadu/`
+folder under this location.
+
+In order to enable HTJ2K decoding, some modifications to the source must be
+made. These are documented in the "Enabling_HT.txt" document in the Kakadu
+package, and for our purpose can be boiled down to the following:
+
+- Uncomment the following line near the top of "fbc_common.h" within the
+  "coresys/fast_coding" sub-directory: `#define FBC_ENABLED`
+- Ensure that the `FBC_NO_ACCELERATION` line below `FBC_ENABLED` is commented
+  out.
+- Rename the `srclib_ht` directory in your Kakadu distribution
+  and replace it with a copy of `altlib_ht_opt`.  For example:
+
+  ```
+  mv srclib_ht srclib_ht_noopt; cp -r altlib_ht_opt srclib_ht
+  ```
+
+Then, move on to building the container:
 
 ```
 docker build -t iipsrv_htj2k:latest .