Update cheatsheets

geth

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# geth
+
+> The go-ethereum command-line interface.
+> More information: <https://geth.ethereum.org>.
+
+- Connect to the main Ethereum network and automatically download the full node:
+
+`geth`
+
+- Connect to the Ropsten test network:
+
+`geth --testnet`
+
+- Create a new account:
+
+`geth account new`
+
+- Enable mining:
+
+`geth --mine`