add docs

docs/src/features/code_src.md

@@ -0,0 +1,15 @@
+# `@code_src` macro
+
+The macro allows you to display source code of a method in-line,
+just like `@code_llvm` and `@code_typed`. Inspired by: 
+https://github.com/JuliaLang/julia/issues/2625#issuecomment-498840808
+
+```julia-repl
+julia> @code_src sum(1:3)
+function sum(r::AbstractRange{<:Real})
+    l = length(r)
+    # note that a little care is required to avoid overflow in l*(l-1)/2
+    return l * first(r) + (iseven(l) ? (step(r) * (l-1)) * (l>>1)
+                                     : (step(r) * l) * ((l-1)>>1))
+end
+```

docs/src/index.md

@@ -19,6 +19,7 @@ Pages = [
     "features/rainbow_brackets.md",
     "features/markdown_highlight.md",
     "features/fzf.md",
+    "features/code_src.md",
     "internals/passes.md"
 ]
 Depth = 1