documentation: expose src/examples in README and website

[soypat]

Some folk need practical examples to start writing code. It would be great if the examples were easily accessible from the README.md, or even better: there was a page on tinygo.org which had the list of examples. It is not clear when starting with tinygo what the examples/... directory is and where it lives. We should make it clearer!

Ideas:

• Add examples link to tinygo.org/getting-started/overview/
• Add examples link to tinygo.org/docs/reference or tinygo.org/docs/tutorials, whichever fits best
• Add text to readme, i.e.: The examples/blinky code is contained under the src/examples directory. this directory contains many other examples to get you up and going with tinygo [add link here]

[sago35]

I think adding a link to examples is a great idea.

I have added links to the following in the article I wrote in Japanese.
On second thought, I should have added it to the official documentation.

• tinygo.org/x/tinygo/src/examples/
• tinygo.org/x/drivers/examples/
• tinygo.org/x/tinyfont/examples/