Fix wording, fix line length, and fix bug in shellscript

Before, top-level .md files would be ignored.

Author: jyn514

ci/check_line_lengths.sh

@@ -10,7 +10,7 @@ if [ "$MAX_LINE_LENGTH" == "" ]; then
 fi
 
 if [ "$1" == "" ]; then
-  files=( src/**/*.md )
+  files=( src/**.md )
 else
   files=( "$@" )
 fi

src/stability.md

@@ -72,7 +72,8 @@ Furthermore this attribute is needed to mark an intrinsic as callable from
 
 To stabilize a feature, follow these steps:
 
-0. Ask a **@T-libs** to start an FCP on the tracking issue and wait for the FCP to complete (with `disposition-merge`).
+0. Ask a **@T-libs** member to start an FCP on the tracking issue and wait for
+   the FCP to complete (with `disposition-merge`).
 1. Change `#[unstable]` to `#[stable(since = "version")]`.
    `version` should be the *current nightly*, i.e. stable+2. You can see which version is
    currently nightly [on Forge](https://forge.rust-lang.org/#current-release-versions).