docs/manual: python is no longer a mandatory dependency

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/prerequisite.txt

@@ -32,7 +32,6 @@ between distributions).
 ** +perl+ (version 5.8.7 or any later)
 ** +tar+
 ** +cpio+
-** +python+ (version 2.7 or any later)
 ** +unzip+
 ** +rsync+
 ** +file+ (must be in +/usr/bin/file+)
@@ -45,6 +44,14 @@ between distributions).
 
 === Optional packages
 
+* Recommended dependencies:
++
+Some features or utilities in Buildroot, like the legal-info, or the
+graph generation tools, have additional dependencies. Although they
+are not mandatory for a simple build, they are still highly recommended:
++
+** +python+ (version 2.7 or any later)
+
 * Configuration interface dependencies:
 +
 For these libraries, you need to install both runtime and development