adding zx install instructions to readme

.gitignore

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+*.swp
+*.swo
+*.beam

README.md

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+# gex = gajumaru exchange
+
+Currently there is only one thing, which is the Gajumaru HTTP Daemon.
+
+## How to run `gex_httpd`
+
+Last updated: September 23, 2025 (PRH).
+
+1.  **Install Erlang and zx/zomp**
+
+    Source: [*Building Erlang 26.2.5 on Ubuntu 24.04*](https://zxq9.com/archives/2905)
+
+    Adapt this to your Linux distribution.
+
+    1.a.    **Install necessary build tools**
+
+            ```bash
+            sudo apt update
+            sudo apt upgrade
+            sudo apt install \
+                gcc curl g++ dpkg-dev build-essential automake autoconf \
+                libncurses-dev libssl-dev flex xsltproc libwxgtk3.2-dev \
+                wget vim git
+            ```
+
+    1.b.    **Put [Kerl](https://github.com/kerl/kerl) somewhere in your
+            `$PATH`**. This is a tool to build Erlang releases.
+
+            ```bash
+            wget -O ~/bin/kerl https://raw.githubusercontent.com/kerl/kerl/master/kerl
+            chmod u+x ~/bin/kerl
+            ```
+
+    1.c.    **Build Erlang from source using Kerl**
+
+            ```bash
+            kerl update releases
+            ## use the most recent one that looks stable
+            ## you do need to type the number twice, that's not a typo
+            kerl build 28.1 28.1
+            kerl install 28.1 ~/.erts/28.1
+            ```
+
+    1.d.    **Put Erlang in your `$PATH`**
+
+            Update .bashrc or .zshrc or whatever with the following line:
+
+            ```bash
+            . $HOME/.erts/28.1/activate
+            ```
+
+
+    1.e.    **Install zx**
+
+            ```bash
+            wget -q https://zxq9.com/projects/zomp/get_zx && bash get_zx
+            ```
+
+    1.f.    **Test zx works**
+
+            zx installs itself to `~/bin`, so make sure that's in your
+            `$PATH`.
+
+            ```bash
+            zx run erltris
+            ```