Update cheatsheets

ninja

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# ninja
+
+> A Build system designed to be fast.
+> More information: <https://ninja-build.org/manual.html>.
+
+- Build in the current directory:
+
+`ninja`
+
+- Build in the current directory, executing 4 jobs at a time in parallel:
+
+`ninja -j {{4}}`
+
+- Build a program in a given directory:
+
+`ninja -C {{path/to/directory}}`
+
+- Show targets (e.g. `install` and `uninstall`):
+
+`ninja -t targets`
+
+- Display help:
+
+`ninja -h`