EDSP doc: (minor) consistently use 2 blank lines before headings

Git-Dch: Ignore

doc/external-dependency-solver-protocol.txt

@@ -70,6 +70,7 @@ configuration documentation for more, and more up to date, information.
 - **Dir::Bin::Solvers**: absolute path of the directory where to look for
   external solvers. Defaults to `/usr/lib/apt/solvers`.
 
+
 ## Protocol
 
 When configured to use an external solver, APT will resort to it to
@@ -226,6 +227,7 @@ field. The following fields are supported in package stanzas:
   Release file entry (Origin, Label, Codename, etc.) in the format of
   APT_PREFERENCES(5).
 
+
 ### Answer
 
 An answer from the external solver to APT is either a *solution* or an