Add example readme

Author: 38

examples/README.md

@@ -1,9 +1,11 @@
 # plotters examples
 
-These are examples of plotters in use! Like in all Rust packages, examples can be built and run with `cargo`.
-
 To run any example, from within the repo, run `cargo run --example <example_name>` where `<example name>` is the name of the file without the `.rs` extension.
 
-The output of these example files are used to generate the [plotters-doc-data](https://github.com/38/plotters-doc-data) repo that populates the beautiful images you see in the main README. For that reason, they must be run with `cargo` from within the repo, or you must change the output filename in the example code to a directory that exists.
+All the examples assumes the directory [plotters-doc-data](https://github.com/38/plotters-doc-data) exists, otherwise those example crashs.
+
+The output of these example files are used to generate the [plotters-doc-data](https://github.com/38/plotters-doc-data) repo that populates the sample images in the main README.
+We also relies on the output of examples to detect protential layout changes.
+For that reason, **they must be run with `cargo` from within the repo, or you must change the output filename in the example code to a directory that exists.**
 
 The examples that have their own directories and `Cargo.toml` files work differently. They are run the same way you would a standalone project.