docs/manual: post-image.sh/post-build.sh should use '-', not '_'

Even though it's only documentation, the form of the names of the
post-image.sh and post-build.sh scripts should be consistent with the
names of those scripts used in the code base, using hyphen, not
underscore.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit c529a2c286)
Signed-off-by: Raphaël Mélotte <raphael.melotte@mind.be>

docs/manual/customize-directory-structure.adoc

@@ -23,8 +23,8 @@ to you.
 |           +-- linux.config
 |           +-- busybox.config
 |           +-- <other configuration files>
-|           +-- post_build.sh
-|           +-- post_image.sh
+|           +-- post-build.sh
+|           +-- post-image.sh
 |           +-- rootfs_overlay/
 |           |   +-- etc/
 |           |   +-- <some files>
@@ -84,7 +84,7 @@ layers 'common' and 'fooboard' is:
 +-- board/
     +-- <company>/
         +-- common/
-        |   +-- post_build.sh
+        |   +-- post-build.sh
         |   +-- rootfs_overlay/
         |   |   +-- ...
         |   +-- patches/
@@ -94,7 +94,7 @@ layers 'common' and 'fooboard' is:
             +-- linux.config
             +-- busybox.config
             +-- <other configuration files>
-            +-- post_build.sh
+            +-- post-build.sh
             +-- rootfs_overlay/
             |   +-- ...
             +-- patches/

docs/manual/customize-quick-guide.adoc

@@ -35,9 +35,9 @@ your project can be skipped.
    Set +BR2_ROOTFS_OVERLAY+
    to +board/<manufacturer>/<boardname>/rootfs-overlay+.
 . Create a post-build script
-   +board/<manufacturer>/<boardname>/post_build.sh+. Set
+   +board/<manufacturer>/<boardname>/post-build.sh+. Set
    +BR2_ROOTFS_POST_BUILD_SCRIPT+ to
-   +board/<manufacturer>/<boardname>/post_build.sh+
+   +board/<manufacturer>/<boardname>/post-build.sh+
 . If additional setuid permissions have to be set or device nodes have
    to be created, create +board/<manufacturer>/<boardname>/device_table.txt+
    and add that path to +BR2_ROOTFS_DEVICE_TABLE+.

docs/manual/customize-rootfs.adoc

@@ -47,7 +47,7 @@ Using post-build scripts, you can remove or modify any file in your
   post-build cleanup scripts.
 +
 As shown in xref:customize-dir-structure[], the recommended path for
-  this script is +board/<company>/<boardname>/post_build.sh+.
+  this script is +board/<company>/<boardname>/post-build.sh+.
 +
 The post-build scripts are run with the main Buildroot tree as current
   working directory. The path to the target filesystem is passed as the