Document possibly surprising syntax for submodule usage

Author: Patrick Häcker

README.md

@@ -17,6 +17,16 @@ using UseAll
 
 After that, names such as `countfrom` can be used directly, without writing `Base.Iterators.countfrom`.
 
+Submodules of the current module are detected automatically, so if you defined a module at the REPL you can write:
+
+```julia
+module MyModule
+    f(x) = x + 1
+end
+
+@useall MyModule   # The Julia parser does not accept `@useall .MyModule` here.
+```
+
 This is useful while working in the REPL: By pulling names from a package or submodule into `Main`, you can execute copy-pasted code from a module. That means all your previous definitions in your REPL session or from your `startup.jl` remain available. You can also add the names from more than one module and can execute their copy-pasted code without doing anything else in-between.
 
 It is also useful in closely coupled code, for example in a package's own `runtests.jl`, where explicit imports can become noisy and the code intentionally works with many internals of the same package.

src/UseAll.jl

@@ -11,9 +11,12 @@ Unlike `using Module`, which only imports the explicitly exported names, `@useal
 all names — including private and imported ones — except for hidden compiler-generated names
 (starting with `#`) and names already present in the target module (such as `eval` and `include`).
 
-Supports top-level packages and submodules:
+Supports top-level packages, submodules, and submodules of the current module:
 
-    @useall TOML Base.Iterators
+    @useall TOML Base.Iterators MyModule
+
+Submodules of the caller's module (e.g. defined in `Main`) are detected automatically:
+use `@useall MyModule` instead of `@useall .MyModule`, as the latter is invalid syntax in Julia.
 
 When [Revise.jl](https://github.com/timholy/Revise.jl) is loaded, newly exported symbols are
 automatically imported after revision.