Updated README with build and install instructions
MODIFY
utils/plot_ui/README.md
utils/plot_ui/README.md
`afl-plot-ui` is a helper utility for rendering the GNUplot graphs in a GTK window. This allows to real time resizing, scrolling, and cursor positioning features while viewing the graph. This utility also provides options to hide graphs using check buttons.
+Currently, this utility is not built by default.
+You can manually build and install `afl-plot-ui` as follows
+
+```shell
+sudo apt install libgtk-3-0 libgtk-3-dev pkg-config
+make
+cd ../../
+sudo make install
+```
+
*NOTE:* This utility is not meant to be used standalone. Never run this utility directly. Always run [`afl-plot`](../../afl-plot), which will, in turn, invoke this utility (when run using `-g` or `--graphical` flag).
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Updated README with build and install instructions