Update README.md

README.md

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-# lean-graph
+# lean-graph
+
+A simple tool to create import graphs of lake packages.
+
+
+## Requirements
+
+For creating different output formats than `.dot` (for example to create a `.pdf` file), you should have `graphviz` installed.
+
+## Usage
+
+You can import this in any lean projects by the following line to your `lakefile.lean`:
+
+```lean
+require importGraph from git "https://github.com/leanprover-community/lean-graph" @ "main"
+```
+
+After running `lake update -R importGraph` in your project, you can create import graphs with
+
+```bash
+lake exe graph
+```
+
+A typical command is `lake exe graph --reduce --to MyModule my_graph.pdf` where `MyModule` follows the same module naming you would use to `import` it in lean.
+See `lake exe graph --help` for more options.