more documentation improve

doc/src/usage.md

@@ -11,7 +11,7 @@ Weave document with markup and julia code using `Plots.jl` for plots,
 > A prepared example
 
 ```julia
-#First add depencies for the example
+# First add depencies for the example
 using Pkg; Pkg.add.(["Plots", "DSP"])
 using Weave
 weave(joinpath(dirname(pathof(Weave)), "../examples", "FIR_design.jmd"), out_path=:pwd)
@@ -26,7 +26,7 @@ weave
 Tangling extracts the code from document:
 
 ```@docs
-tangle(source)
+tangle
 ```
 
 ## Supported output formats

src/Weave.jl

@@ -21,7 +21,11 @@ end
 
 
 """
-    tangle(source; out_path=:doc, informat=:auto)
+    tangle(
+        source::AbstractString;
+        out_path::Union{Symbol,AbstractString} = :doc,
+        informat::Union{Symbol,AbstractString} = :auto
+    )
 
 Tangle source code from input document to .jl file.
 
@@ -34,7 +38,7 @@ Tangle source code from input document to .jl file.
   * `"somepath"`: `String` of output directory e.g. `"~/outdir"`, or of filename e.g. `"~/outdir/outfile.tex"`
 """
 function tangle(
-    source;
+    source::AbstractString;
     out_path::Union{Symbol,AbstractString} = :doc,
     informat::Union{Symbol,AbstractString} = :auto
 )