Improve clarity of mod terminology (#37656)

"mainline mod" is confusing as the mods in the repository are not part
of the main game. Thus such mods are now labeled as being in the
CleverRaven repository or simply "in-repo"

doc/MAINLINE_MODS.md → doc/IN_REPO_MODS.md

@@ -2,21 +2,21 @@
 
 Cataclysm: Dark Days Ahead is not only moddable, but ships with a number of mods available for users to select from even without having to obtain mods from a third party source.
 
-## Why have mainlined mods?
+## Why have in-repo mods?
 
-The benefits of having mods mainlined include:
+The benefits of having mods in the repository include:
 
 *  Visibility to a large number of users and potential contributors
 *  The ability to use the CleverRaven issue tracker to report problems, as well as manage pull requests for adding to or fixing mods in the repository
-*  Mods in mainline that demonstrate usage of a game feature which exists only for mods (i.e. not used by the core DDA game itself) help ensure that feature stays present in the game.
+*  Mods in the CleverRaven repository that demonstrate usage of a game feature which exists only for mods (i.e. not used by the core DDA game itself) help ensure that feature stays present in the game.
 
 There are however things that might be expected but are not guaranteed:
 
 *  Guarantee of maintenance of content -- core devs are mostly focused on the main game itself; although some might pick up mods as a side task, people who continue working on the core game tend to like the feel of the core game.
 *  Guarantee of maintenance of used features -- over the course of development it may become impossible to keep a feature, due to performance needs or maintenance burden.
 *  Guarantee of sole authorship -- once in the repository, the mod is considered community content. While the developers might defer to an active maintainer of a mod, if they become inactive anyone else can step forward.
 
-## What kind of mods can be in the repository as mainlined mods?
+## What kind of mods can be in the CleverRaven repository?
 
 There are three primary categories of mods:
 
@@ -38,7 +38,7 @@ Furthermore, there are additional criteria:
 
 A mod maintainer's role is to curate additions to mods and ensure they fit the concept of the mod.  Maintainers are also responsible for at least acknowledging bug reports related to the mod: while maintainers don't have to personally manage every bugfix, if a bug is reported, the maintainer should be around to comment and help to find someone to fix it.
 
-It's important to understand that if a mod is part of mainline, it is expected that people other than the maintainer are going to contribute to it, as with anything.  On github, mod maintainers should Approve or Request Changes on PRs to the mod.  If the maintainer has approved it, developers with merge permissions will treat that as a request to merge the changes.
+It's important to understand that if a mod is in the repository, it is expected that people other than the maintainer are going to contribute to it, as with anything.  On github, mod maintainers should Approve or Request Changes on PRs to the mod.  If the maintainer has approved it, developers with merge permissions will treat that as a request to merge the changes.
 
 ## When do mods get removed?
 
@@ -50,10 +50,10 @@ Whenever a stable release occurs, mods which no longer qualify for inclusion wil
 
 While it may be counterintuitive, simply having a mod in the repository increases maintenance burden for the team, even for the people who don't use the mods itself.
 
-Furthermore, mods which are in mainline but are not working correctly for whatever reason reflect poorly on the project on the whole. While it might seem 'easy' to fix a mod, the development team is mostly focused on the core game itself. This is why mod maintainers are necessary.
+Furthermore, mods which are shipped with the game but are not working correctly for whatever reason reflect poorly on the project on the whole. While it might seem 'easy' to fix a mod, the development team is mostly focused on the core game itself. This is why mod maintainers are necessary.
 
 ## How can mods be rescued from removal?
 
 If the mod otherwise meets inclusion criteria but lacks a maintainer (ie. has been declared orphaned), it's as simple as having someone else step forward as the new maintainer.
 
-Otherwise, it needs to either be made to meet the criteria, or it simply isn't going to be staying in mainline.
+Otherwise, it needs to either be made to meet the criteria, or it simply isn't going to be staying in the CleverRaven repository.