Update cheatsheets

tldr/sfdk-build-shell

@@ -0,0 +1,22 @@
+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# sfdk build-shell
+
+> Executes custom steps in build engine.
+> See also: `sfdk config` for configuring the build target and `sfdk build-init` for initializing build tree.
+> More information: <https://docs.sailfishos.org/Develop/Apps/Tutorials/Building_packages_-_advanced_techniques/>.
+
+- Launch interactive shell in the build engine:
+
+`sfdk build-shell`
+
+- Run a specified command in the build shell:
+
+`sfdk build-shell {{command}}`
+
+- Launch interactive shell in the build engine in maintenance mode, when inspecting or modifying the build environment:
+
+`sfdk build-shell --maintain`