x86_64, uname26, linux32, linux64, i386: add page (#15374)

* Create x86_64.md

* Update x86_64.md

* Create uname26.md

* Create linux32.md

* Create linux64.md

* Create i386.md

pages/linux/linux64.md

@@ -0,0 +1,7 @@
+# linux64
+
+> This command is an alias of `setarch linux64`.
+
+- View documentation for the original command:
+
+`tldr setarch`