add docs

Diagnostic-information.md

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+SQLite running in sqliteviz is compiled with particular [options][1] that can
+enable or disable some SQLite features. You can get a list of them in `App
+info` dialog (fig. 1) by clicking on <img src="./img/info.svg"/> icon in the top
+toolbar.
+
+<p align="center">
+  <img class="figure" src="./img/Screenshot_app_info.png?0.13.0"/>
+</p>
+
+<p align="center">
+  <sub>
+    Fig. 1: App info dialog
+  </sub>
+</p>
+
+[1]: https://sqlite.org/compile.html