watchexec: add page (#4061)

pages/common/watchexec.md

@@ -0,0 +1,20 @@
+# watchexec
+
+> Run arbitrary commands when files change.
+> More information: <https://github.com/watchexec/watchexec>.
+
+- Call `ls -la` when any file in the current directory changes:
+
+`watchexec -- {{ls -la}}`
+
+- Run `make` when any JavaScript, CSS and HTML files in the current directory change:
+
+`watchexec --exts {{js,css,html}} make`
+
+- Run `make` when any file in the `lib` or `src` subdirectories change:
+
+`watchexec --watch {{lib}} --watch {{src}} {{make}}`
+
+- Call/restart `my_server` when any file in the current directory change, sending `SIGKILL` to stop the child process:
+
+`watchexec --restart --signal {{SIGKILL}} {{my_server}}`