dex/testing: Add more info about required harness execs (#3531)

Signed-off-by: Philemon Ukane <ukanephilemon@gmail.com>

Author: ukane-philemon

dex/testing/btc/README.md

@@ -23,6 +23,8 @@ outputs, but has a number of UTXOs of varying size and confirmation count.
 You must have [bitcoind and bitcoin-cli](https://github.com/bitcoin/bitcoin/releases)
 in `PATH` to use the harness. Bitcoin Core v26.0.0+ is recommended. v30+ is fully supported.
 
+To get `bitcoind` and `bitcoin-cli`, you must download only a `.tar.gz` for the operating system you choose. Then extract the `.tar.gz` file to find the `bin` folder and add the `bin` folder to `PATH`.
+
 It also requires tmux.
 
 ## Harness control scripts

dex/testing/dcr/README.md

@@ -11,6 +11,12 @@ The harness depends on [dcrd](https://github.com/decred/dcrd), [dcrwallet](https
 
 You must have `dcrd` `dcrwallet` and `dcrctl` in `PATH` to use the harness.
 
+All of the above can be downloaded at once from [Decred Binaries Release Page](https://github.com/decred/decred-binaries/releases).
+
+Download the `Decred-{os}-{architecture}-{version}` file with a `.tar.gz` extension and extract it to find all the executables you need. 
+
+Then add the path to those executables in `PATH`.
+
 The harness script will create two connected simnet nodes and wallets, and
 then mine some blocks and send some regular transactions. The result is a set of
 wallets named **alpha** and **beta**, each with slightly different properties.