Update cheatsheets

tldr/linux/valheim

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# Valheim
+
+> Create and start a headless Valheim server.
+> Note: Configure the server by editing a copy of the `start_server.sh` script.
+> More information: <https://www.valheimgame.com/support/a-guide-to-dedicated-servers/>.
+
+- Start the server:
+
+`{{path/to/start_server.sh}}`
+
+- Stop the server gracefully:
+
+`<Ctrl c>`
+
+- Start the server using the provided Docker script:
+
+`{{path/to/docker_start_server.sh}} {{path/to/start_server.sh}}`