opt: add page (#2527)

pages/common/opt.md

@@ -0,0 +1,15 @@
+# opt
+
+> A tool that takes LLVM source files and runs specified optimizations and/or analyses on them.
+
+- Run an optimization or analysis on a bitcode file:
+
+`opt -{{passname}} {{path/to/file.bc}} -S -o {{file_opt.bc}}`
+
+- Output the Control Flow Graph of a function to a "dot" file:
+
+`opt {{-dot-cfg}} -S {{path/to/file.bc}} -disable-output`
+
+- Optimize the program at level 2 and output the result to another file:
+
+`opt -O2 {{path/to/file.bc}} -S -o {{path/to/output_file.bc}}`