fix(edit): require subr-x in klammertext-align.el (Emacs 27)

klammertext-align.el calls string-trim, string-blank-p, and
string-empty-p without requiring subr-x.  Newer Emacs has that library
loaded already; on Emacs 27 -- what Ubuntu 22.04 and Pop!_OS 22.04 ship
-- the symbols are void and table alignment fails with "Symbol's
function definition is void: string-blank-p".  The README now states
Emacs 27.1 as the supported floor.

(from dev 43a4ce7dea2a)

README.md

@@ -41,7 +41,7 @@ are regenerated on each release — patches cannot be merged directly.
 Report problems (or send patches) to the author; accepted changes are
 applied to the development tree and appear in a following snapshot.
 
-This snapshot was assembled from development commit `ca9eaa2c867a`.
+This snapshot was assembled from development commit `43a4ce7dea2a`.
 
 ## License