Update outdated documentation

The part of the documentation about handling of transitive package
dependencies was no longer correct since commit dfeed75. Now it is
updated to describe the new behavior.

Related to nim-lang#127

readme.markdown

@@ -228,11 +228,11 @@ query parameter. For example:
 ### nimble develop
 
 The develop command is used for putting packages in a development mode. When
-executed with a list of packages it clones their repository. If it is
-executed in a package directory it adds cloned packages to the special
-`nimble.develop` file. This is a special file which is used for holding the
-paths to development mode dependencies of the current directory package. It has
-the following structure:
+executed with a list of packages it clones their repository. If it is executed
+in a package directory it adds cloned packages to the special `nimble.develop`
+file. This is a special file which is used for holding the paths to development
+mode dependencies of the current directory package. It has the following
+structure:
 
 ```json
 {
@@ -247,17 +247,15 @@ the following structure:
 * `dependencies` - JSON array of paths to Nimble packages directories.
 
 The format for included develop files is the same as the project's develop
-file, but their validation works slightly different.
+file.
 
-Validation rules:
+Develop files validation rules:
 
 * The included develop files must be valid.
-* The packages listed in `dependencies` section must be dependencies required
-by the package's `.nimble` file and to be in the required by its version range.
-Transitive dependencies are not allowed, but this may be changed in the future.
-* The packages listed in the included develop files are required to be valid
-**Nimble** packages, but they are not required to be valid dependencies of the
-current project. In the latter case, they are simply ignored.
+* The packages listed in the `dependencies` section and in the included develop
+files are required to be valid **Nimble** packages, but they are not required
+to be valid dependencies of the current project. In the latter case, they are
+simply ignored.
 * The develop files of the develop mode dependencies of a package are being
 followed and processed recursively. Finally, only one common set of develop
 mode dependencies is created.
@@ -300,16 +298,6 @@ executing `develop` command from some package's directory unless
 Because the develop files are user-specific and they contain local file system
 paths they **MUST NOT** be committed.
 
-**Current limitations:**
-
-* Currently transitive dependencies in the `dependencies` section of the
-develop file are not allowed. In the future, they should be allowed because
-this will allow using in develop mode some transitive package dependencies
-without having in develop mode the full dependency tree path to them. It was a
-design mistake that was not allowed at the beginning. The current workaround is
-to add the transitive dependency as a dependency in the project's `.nimble`
-file.
-
 ### nimble lock
 
 The `nimble lock` command will generate or update a package lock file named