Fixes TRJReader random frame access docs (#2595)

* Fixes #2398

* Update CHANGELOG

package/CHANGELOG

@@ -21,6 +21,8 @@ mm/dd/yy richardjgowers, kain88-de, lilyminium, p-j-smith, bdice, joaomcteixeira
   * 0.21.0
 
 Fixes
+  * Fixes outdated :class:`TRJReader` documentation on random frame access
+    (Issue #2398)
   * Fixed mda.Merge for Universes without coordinates (Issue #2470)(PR #2580)
   * PCA(align=True) now correctly aligns the trajectory and computes the
     correct means and covariance matrix (Issue #2561)

package/MDAnalysis/coordinates/TRJ.py

@@ -120,9 +120,6 @@
 * The trajectory does not contain time information so we simply set
   the time step to 1 ps (or the user could provide it as kwarg *dt*)
 
-* **No direct access of frames is implemented, only iteration through
-  the trajectory.**
-
 * Trajectories with fewer than 4 atoms probably fail to be read (BUG).
 
 * If the trajectory contains exactly *one* atom then it is always
@@ -204,9 +201,6 @@ class TRJReader(base.ReaderBase):
     be set by passing the `dt` keyword argument to the constructor; it
     is assumed to be in ps. The default value is 1 ps.
 
-    Functionality is currently limited to simple iteration over the
-    trajectory.
-
     .. _AMBER TRJ format: http://ambermd.org/formats.html#trajectory
 
     .. versionchanged:: 0.11.0