jr: add build instructions to readme

jrx/README.md

@@ -7,6 +7,23 @@ meant to work in the latest versions of Firefox and Chromium.
 
 Requires [jex](../utils/jex).
 
+1.  You need to install JR's dependencies. These are listed in the `jex.eterms`
+    file. As of March 18, 2024, all of JR's dependencies can be found in the
+    `../libs/` directory.
+
+    For instance, to install `awcp`, you do
+
+    ```
+    cd ../libs/awcp
+    jex dwim+
+    ```
+
+    There is a command called `jex install` which is a synonym for `jex
+    dwim++`. This attempts to also build and install package documentation, and
+    this doesn't work for every dependency (in particular, the `tweetnacl`
+    dependency).  `jex dwim+` should work in every case.
+
+2. Build JR
 ```
 jex dwim-
 ```